Fix filter to be treated the same as function in LSP outline view

- Add explicit comment in VisitFunctionDefinition clarifying filter
  gets SymbolType.Function so it participates in the outline hierarchy
  the same way regular functions do (children expand correctly)
- Update MultipleSymbols.ps1 test data so AFilter has a local variable
  declaration ($FilterVar = $_), exercising filter-with-children path
- Update FindsSymbolsInFile test counts and add assertion verifying
  $FilterVar inside a filter is tracked as a declaration (prerequisite
  for it appearing as a child of the filter in the outline)

Agent-Logs-Url: https://github.com/PowerShell/PowerShellEditorServices/sessions/89bcabc2-3cb5-470a-8d43-bcc6adaf0c30

Co-authored-by: JustinGrote <15258962+JustinGrote@users.noreply.github.com>

Author: Copilot

src/PowerShellEditorServices/Services/Symbols/Visitors/SymbolVisitor.cs

@@ -50,6 +50,8 @@ public override AstVisitAction VisitCommand(CommandAst commandAst)
 
     public override AstVisitAction VisitFunctionDefinition(FunctionDefinitionAst functionDefinitionAst)
     {
+        // Treat filter the same as function: both get SymbolType.Function so they appear in the
+        // outline and support child symbols (variables, nested functions, etc.) in the hierarchy.
         SymbolType symbolType = functionDefinitionAst.IsWorkflow
             ? SymbolType.Workflow
             : SymbolType.Function;

test/PowerShellEditorServices.Test.Shared/Symbols/MultipleSymbols.ps1

@@ -6,7 +6,7 @@ $Script:ScriptVar2 = 2
 
 function script:AFunction {}
 
-filter AFilter {$_}
+filter AFilter { $FilterVar = $_ }
 
 function AnAdvancedFunction {
     begin {

test/PowerShellEditorServices.Test/Language/SymbolsServiceTests.cs

@@ -773,9 +773,9 @@ public void FindsSymbolsInFile()
             IEnumerable<SymbolReference> symbols = FindSymbolsInFile(FindSymbolsInMultiSymbolFile.SourceDetails);
 
             Assert.Equal(7, symbols.Count(i => i.Type == SymbolType.Function));
-            Assert.Equal(8, symbols.Count(i => i.Type == SymbolType.Variable));
+            Assert.Equal(9, symbols.Count(i => i.Type == SymbolType.Variable));
             Assert.Equal(4, symbols.Count(i => i.Type == SymbolType.Parameter));
-            Assert.Equal(12, symbols.Count(i => i.Id.StartsWith("var ")));
+            Assert.Equal(13, symbols.Count(i => i.Id.StartsWith("var ")));
             Assert.Equal(2, symbols.Count(i => i.Id.StartsWith("prop ")));
 
             SymbolReference symbol = symbols.First(i => i.Type == SymbolType.Function);
@@ -788,6 +788,12 @@ public void FindsSymbolsInFile()
             Assert.Equal("filter AFilter ()", symbol.Name);
             Assert.True(symbol.IsDeclaration);
 
+            // Verify that a variable declared inside a filter is tracked as a declaration,
+            // allowing it to appear as a child of the filter in the LSP outline hierarchy.
+            symbol = Assert.Single(symbols, i => i.Id == "var FilterVar");
+            Assert.Equal("$FilterVar", symbol.Name);
+            Assert.True(symbol.IsDeclaration);
+
             symbol = symbols.Last(i => i.Type == SymbolType.Variable);
             Assert.Equal("var nestedVar", symbol.Id);
             Assert.Equal("$nestedVar", symbol.Name);