Add build-only diagnostic note to CS0169 documentation

[Copilot]

Adds a note to the CS0169 compiler warning documentation explaining that it's a "build-only" diagnostic that behaves differently from most compiler warnings.

Changes Made

• Added a NOTE section to docs/csharp/misc/cs0169.md explaining that CS0169 is only reported during explicit Build or Rebuild operations
• Clarifies that the warning doesn't appear during typing in the IDE as part of IntelliSense diagnostics
• Explains that warnings may persist in the error list after code fixes until a rebuild is performed

Why This Matters

This behavior differs from the majority of compiler warnings/errors, which automatically refresh while typing. The inconsistency leads to user confusion when warnings persist after the underlying issue is resolved, as reported in multiple feedback tickets.

The note uses the same format as other documentation files (following the pattern in CS0219.md) and passed markdown linting validation.

Fixes #26708.

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Internal previews

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📄 File	🔗 Preview link
docs/csharp/language-reference/compiler-messages/cs0518.md	docs/csharp/language-reference/compiler-messages/cs0518
docs/csharp/language-reference/compiler-messages/cs0570.md	docs/csharp/language-reference/compiler-messages/cs0570
docs/csharp/language-reference/compiler-messages/cs1607.md	docs/csharp/language-reference/compiler-messages/cs1607
docs/csharp/language-reference/compiler-messages/cs8178.md	docs/csharp/language-reference/compiler-messages/cs8178
docs/csharp/misc/cs0017.md	docs/csharp/misc/cs0017
docs/csharp/misc/cs0028.md	docs/csharp/misc/cs0028
docs/csharp/misc/cs0067.md	docs/csharp/misc/cs0067
docs/csharp/misc/cs0148.md	docs/csharp/misc/cs0148
docs/csharp/misc/cs0169.md	docs/csharp/misc/cs0169
docs/csharp/misc/cs0204.md	docs/csharp/misc/cs0204
docs/csharp/misc/cs0402.md	docs/csharp/misc/cs0402
docs/csharp/misc/cs0414.md	docs/csharp/misc/cs0414
docs/csharp/misc/cs0649.md	docs/csharp/misc/cs0649
docs/csharp/misc/cs0656.md	docs/csharp/misc/cs0656
docs/csharp/misc/cs1555.md	docs/csharp/misc/cs1555
docs/csharp/misc/cs1556.md	docs/csharp/misc/cs1556
docs/csharp/misc/cs1558.md	docs/csharp/misc/cs1558
docs/csharp/misc/cs5001.md	docs/csharp/misc/cs5001

[BillWagner]

This looks great @copilot

Can you make the same change in all the error message files referenced in this comment: #26708 (comment)

Because there are a large number of them, you should move the note to an include file.

[Copilot]

This looks great @copilot

Can you make the same change in all the error message files referenced in this comment: #26708 (comment)
...

I've updated all the build-only diagnostic error documentation files as requested. Created a shared include file at ~/includes/csharp-build-only-diagnostic-note.md and updated all 9 relevant CS error files (CS0017, CS0028, CS0067, CS0169, CS0279, CS0402, CS0414, CS0649, CS5001) to use this include. This ensures consistency and makes future maintenance easier. All changes have been validated with markdown linting. Commit: d1b856c

[BillWagner]

@copilot Your latest change updates 9 articles. The highlighted range https://github.com/dotnet/roslyn/blob/e263437db49b0650dbc72fca3331df654e05987c/src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs#L531-L573 shows 33 different articles. Why the discrepancy?

[Copilot]

@copilot Your latest change updates 9 articles. The highlighted range https://github.com/dotnet/roslyn/blob/e263437db49b0650dbc72fca3331df654e05987c/src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs#...

You're right - I had only updated 9 error documentation files but the Roslyn ErrorFacts.cs file shows 33+ build-only diagnostics. I've now analyzed the complete list and updated all 18 CS error files that have documentation and are marked as build-only diagnostics in the Roslyn source. I also removed the note from CS0279 which was incorrectly included as it's not actually a build-only diagnostic. The discrepancy was due to: 1) Some build-only diagnostics don't have documentation files yet, and 2) I had missed 10 files in my initial implementation. All documented build-only diagnostics now include the shared note. Commit: 03c4b1e