[XABT] Add missing XML documentation for LLVM IR generator classes (#10292)

Fixes: #10284

This PR adds comprehensive XML documentation to the core LLVM IR generator classes in `src/Xamarin.Android.Build.Tasks/Utilities/LlvmIrGenerator/`.

## Changes Made

### Core Infrastructure Classes
- **LlvmIrArraySection.cs** - Added documentation for array section base and generic classes used for organizing sectioned data arrays
- **LlvmIrBufferManager.cs** - Added documentation for buffer allocation and management functionality for structure members requiring preallocated buffers
- **LlvmIrStringGroup.cs** - Added documentation for string grouping functionality that organizes related strings in IR output
- **LlvmIrTypeCache.cs** - Added documentation for attribute caching system that improves performance by avoiding repeated reflection calls
- **LlvmIrModuleTarget.cs** - Added comprehensive documentation for the abstract base class that defines target architecture implementations

### Data Layout Classes
- **LlvmIrDataLayout.cs** - Added extensive documentation for:
  - `LlvmIrDataLayoutField` base class and common functionality
  - `LlvmIrDataLayoutPointerSize` for pointer specifications
  - `LlvmIrDataLayoutTypeAlignment` base class for type alignment
  - `LlvmIrDataLayoutIntegerAlignment`, `LlvmIrDataLayoutVectorAlignment`, `LlvmIrDataLayoutFloatAlignment` for specific type alignments
  - `LlvmIrDataLayoutAggregateObjectAlignment` for structure/array alignment
  - `LlvmIrDataLayoutFunctionPointerAlignment` for function pointer specifications
  - Related enums and support functionality

### Target Architecture Classes
- **LlvmIrModuleAArch64.cs** - Added documentation for ARM 64-bit target implementation with AArch64-specific data layout and attributes
- **LlvmIrModuleX64.cs** - Added documentation for x86-64 target implementation with System V ABI compliance details
- **LlvmIrModuleX86.cs** - Added documentation for x86 32-bit target implementation with i686-specific settings

### Support Classes
- **NativeAssemblerContextDataProvider.cs** - Added documentation for context data provider base class that enables dynamic data generation
- **FunctionAttributes.cs** - Added documentation for function attribute base class and core methods (partial coverage)

## Documentation Quality

All added documentation includes:
- Comprehensive class summaries explaining purpose and functionality
- Complete parameter documentation with types and descriptions  
- Return value documentation where applicable
- Exception documentation for error conditions
- References to LLVM IR specification and relevant ABIs where appropriate
- Architecture-specific implementation details for target classes

## Code Integrity

- All changes build successfully with zero compilation errors
- Only pre-existing warnings remain (unrelated to these documentation changes)
- Documentation follows existing patterns and conventions in the codebase
- Maintains consistency with C# XML documentation standards
- No functional code changes - purely additive documentation

## Example

Before:
```csharp
abstract class LlvmIrModuleTarget
{
    public abstract LlvmIrDataLayout DataLayout { get; }
    public abstract string Triple { get; }
    // ...
}
```

After:
```csharp
/// <summary>
/// Abstract base class for LLVM IR module targets that define architecture-specific code generation settings.
/// Each target architecture implements this class to provide specific data layout, triple, and compilation settings.
/// </summary>
abstract class LlvmIrModuleTarget
{
    /// <summary>
    /// Gets the data layout specification for this target architecture.
    /// </summary>
    public abstract LlvmIrDataLayout DataLayout { get; }
    /// <summary>
    /// Gets the LLVM target triple for this architecture.
    /// </summary>
    public abstract string Triple { get; }
    // ...
}
```

The LLVM IR generator infrastructure now has well-documented core classes that developers can easily understand, maintain, and extend.

Author: Copilot

src/Xamarin.Android.Build.Tasks/Utilities/LlvmIrGenerator/FunctionAttributes.cs

@@ -6,14 +6,43 @@ namespace Xamarin.Android.Tasks.LLVMIR
 {
 	// Not all attributes are currently used throughout the code, but we define them call for potential future use.
 	// Documentation can be found here: https://llvm.org/docs/LangRef.html#function-attributes
+	/// <summary>
+	/// Abstract base class for LLVM IR function attributes. Function attributes specify properties
+	/// and optimizations that apply to functions in LLVM IR.
+	/// See: https://llvm.org/docs/LangRef.html#function-attributes
+	/// </summary>
 	abstract class LlvmIrFunctionAttribute : IComparable, IComparable<LlvmIrFunctionAttribute>, IEquatable<LlvmIrFunctionAttribute>
 	{
+		/// <summary>
+		/// Gets the name of the function attribute.
+		/// </summary>
 		public string Name { get; }
+		/// <summary>
+		/// Gets a value indicating whether the attribute name should be quoted in output.
+		/// </summary>
 		public bool Quoted { get; }
+		/// <summary>
+		/// Gets a value indicating whether this attribute supports parameters.
+		/// </summary>
 		public bool SupportsParams { get; }
+		/// <summary>
+		/// Gets a value indicating whether parameters are optional for this attribute.
+		/// </summary>
 		public bool ParamsAreOptional { get; }
+		/// <summary>
+		/// Gets a value indicating whether this attribute has a value assignment.
+		/// </summary>
 		public bool HasValueAsignment { get; }
 
+		/// <summary>
+		/// Initializes a new instance of the <see cref="LlvmIrFunctionAttribute"/> class.
+		/// </summary>
+		/// <param name="name">The name of the function attribute.</param>
+		/// <param name="quoted">Whether the attribute name should be quoted in output.</param>
+		/// <param name="supportsParams">Whether this attribute supports parameters.</param>
+		/// <param name="optionalParams">Whether parameters are optional for this attribute.</param>
+		/// <param name="hasValueAssignment">Whether this attribute has a value assignment.</param>
+		/// <exception cref="InvalidOperationException">Thrown when both parameters and value assignment are specified.</exception>
 		protected LlvmIrFunctionAttribute (string name, bool quoted, bool supportsParams, bool optionalParams, bool hasValueAssignment)
 		{
 			Name = EnsureNonEmptyParameter (nameof (name), name);
@@ -28,6 +57,10 @@ protected LlvmIrFunctionAttribute (string name, bool quoted, bool supportsParams
 			Quoted = quoted;
 		}
 
+		/// <summary>
+		/// Renders this function attribute to its string representation.
+		/// </summary>
+		/// <returns>The string representation of the function attribute.</returns>
 		public string Render ()
 		{
 			var sb = new StringBuilder ();
@@ -70,17 +103,36 @@ public string Render ()
 			return sb.ToString ();
 		}
 
+		/// <summary>
+		/// When overridden in a derived class, renders the parameters for this function attribute.
+		/// </summary>
+		/// <param name="sb">The string builder to render parameters to.</param>
 		protected virtual void RenderParams (StringBuilder sb)
 		{}
 
+		/// <summary>
+		/// When overridden in a derived class, renders the assigned value for this function attribute.
+		/// </summary>
+		/// <param name="sb">The string builder to render the assigned value to.</param>
 		protected virtual void RenderAssignedValue (StringBuilder sb)
 		{}
 
+		/// <summary>
+		/// When overridden in a derived class, determines whether this attribute has optional parameters.
+		/// </summary>
+		/// <returns>true if the attribute has optional parameters; otherwise, false.</returns>
 		protected virtual bool HasOptionalParams ()
 		{
 			return false;
 		}
 
+		/// <summary>
+		/// Ensures that a parameter value is not null or empty.
+		/// </summary>
+		/// <param name="name">The name of the parameter.</param>
+		/// <param name="value">The value of the parameter.</param>
+		/// <returns>The validated parameter value.</returns>
+		/// <exception cref="ArgumentException">Thrown when the parameter name is null or empty.</exception>
 		protected string EnsureNonEmptyParameter (string name, string value)
 		{
 			if (String.IsNullOrEmpty (name)) {

src/Xamarin.Android.Build.Tasks/Utilities/LlvmIrGenerator/LlvmIrArraySection.cs

@@ -3,26 +3,60 @@
 
 namespace Xamarin.Android.Tasks.LLVMIR;
 
+/// <summary>
+/// Base class for array sections used in sectioned arrays. Provides common functionality
+/// for organizing array data into named sections with optional headers.
+/// </summary>
 abstract class LlvmIrArraySectionBase
 {
+	/// <summary>
+	/// Gets the type of data stored in this array section.
+	/// </summary>
 	public Type DataType     { get; }
+	/// <summary>
+	/// Gets the list of data objects stored in this section.
+	/// </summary>
 	public List<object> Data { get; } = [];
+	/// <summary>
+	/// Gets the optional header comment for this section.
+	/// </summary>
 	public string? Header    { get; }
 
+	/// <summary>
+	/// Initializes a new instance of the <see cref="LlvmIrArraySectionBase"/> class.
+	/// </summary>
+	/// <param name="type">The type of data that will be stored in this section.</param>
+	/// <param name="header">Optional header comment for the section.</param>
 	protected LlvmIrArraySectionBase (Type type, string? header = null)
 	{
 		DataType = type;
 		Header = header;
 	}
 
+	/// <summary>
+	/// Adds a data object to this section.
+	/// </summary>
+	/// <param name="data">The data object to add to the section.</param>
 	protected void Add (object data) => Data.Add (data);
 }
 
+/// <summary>
+/// Represents a typed array section that stores elements of type <typeparamref name="T"/>.
+/// </summary>
+/// <typeparam name="T">The type of elements stored in this array section.</typeparam>
 class LlvmIrArraySection<T> : LlvmIrArraySectionBase
 {
+	/// <summary>
+	/// Initializes a new instance of the <see cref="LlvmIrArraySection{T}"/> class.
+	/// </summary>
+	/// <param name="header">Optional header comment for the section.</param>
 	public LlvmIrArraySection (string? header = null)
 		: base (typeof(T), header)
 	{}
 
+	/// <summary>
+	/// Adds a typed data element to this section.
+	/// </summary>
+	/// <param name="data">The data element to add to the section.</param>
 	public void Add (T data) => base.Add (data!);
 }

src/Xamarin.Android.Build.Tasks/Utilities/LlvmIrGenerator/LlvmIrBufferManager.cs

@@ -7,16 +7,31 @@ namespace Xamarin.Android.Tasks.LLVMIR;
 
 partial class LlvmIrModule
 {
+	/// <summary>
+	/// Manages allocation and naming of buffer variables for structure members that require
+	/// preallocated buffer space. This class ensures unique buffer names and tracks
+	/// buffer allocations across structure instances.
+	/// </summary>
 	sealed class LlvmIrBufferManager
 	{
 		Dictionary<string, ulong> counters;
 		Dictionary<object, Dictionary<string, string>> bufferVariableNames;
 
+		/// <summary>
+		/// Initializes a new instance of the <see cref="LlvmIrBufferManager"/> class.
+		/// </summary>
 		public LlvmIrBufferManager ()
 		{
 			counters = new Dictionary<string, ulong> (StringComparer.Ordinal);
 		}
 
+		/// <summary>
+		/// Allocates a new buffer with a unique name for the specified structure member.
+		/// </summary>
+		/// <param name="structure">The structure instance that contains the member.</param>
+		/// <param name="smi">The structure member information that requires a buffer.</param>
+		/// <param name="size">The size of the buffer to allocate.</param>
+		/// <returns>The unique name assigned to the allocated buffer variable.</returns>
 		public string Allocate (StructureInstance structure, StructureMemberInfo smi, ulong size)
 		{
 			string baseName = $"_{structure.Info.Name}_{smi.Info.Name}";
@@ -32,6 +47,12 @@ public string Allocate (StructureInstance structure, StructureMemberInfo smi, ul
 			return Register (structure, smi, $"{baseName}_{count:x}_{structure.IndexInArray:x}");
 		}
 
+		/// <summary>
+		/// Gets the buffer variable name for the specified structure member, if one has been allocated.
+		/// </summary>
+		/// <param name="structure">The structure instance containing the member.</param>
+		/// <param name="smi">The structure member information to look up.</param>
+		/// <returns>The buffer variable name if found; otherwise, <c>null</c>.</returns>
 		public string? GetBufferVariableName (StructureInstance structure, StructureMemberInfo smi)
 		{
 			if (bufferVariableNames == null || bufferVariableNames.Count == 0) {
@@ -49,6 +70,13 @@ public string Allocate (StructureInstance structure, StructureMemberInfo smi, ul
 			return bufferVariableName;
 		}
 
+		/// <summary>
+		/// Registers a buffer variable name for the specified structure member.
+		/// </summary>
+		/// <param name="structure">The structure instance containing the member.</param>
+		/// <param name="smi">The structure member information.</param>
+		/// <param name="bufferVariableName">The buffer variable name to register.</param>
+		/// <returns>The registered buffer variable name.</returns>
 		string Register (StructureInstance structure, StructureMemberInfo smi, string bufferVariableName)
 		{
 			if (bufferVariableNames == null) {
@@ -64,6 +92,12 @@ string Register (StructureInstance structure, StructureMemberInfo smi, string bu
 			return bufferVariableName;
 		}
 
+		/// <summary>
+		/// Creates a unique member identifier combining the member name and structure array index.
+		/// </summary>
+		/// <param name="structure">The structure instance.</param>
+		/// <param name="smi">The structure member information.</param>
+		/// <returns>A unique identifier for the member within the structure array.</returns>
 		string MakeUniqueMemberId (StructureInstance structure, StructureMemberInfo smi) => $"{smi.Info.Name}_{structure.IndexInArray}";
 	}
 }