Add trim analyzer support for C# 14 extensions

[sbomer]

Fixes #115949

This adds Roslyn analyzer support for C# 14 extensions. A few notes on the behavior:

• DAM is supported on method return/params, including on property accessor return/param.
• DAM is not supported on extension properties (see DAM on extension properties is silently ignored #119113)
• DAM is not supported on extension methods (this produces IL2041)
• There's still a bug with the behavior for ILLink/ILC due to the annotations not being preserved into the implementation when lowering: "return" attributes on extension property accessors not emitted on implementation roslyn#80017.

New tests uncovered an analyzer issue with operators in the (extension or not): #119110. This change includes test coverage for non-extension operators.

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[Copilot]

Pull Request Overview

This PR adds trim analyzer support for C# 14 extensions by implementing comprehensive handling of the new extension syntax introduced in C# 14. The key changes enable proper data flow analysis and warning generation for extension members while addressing compiler-generated artifacts.

• Adds test coverage for both traditional extension methods and new C# 14 extension members
• Updates the trim analysis infrastructure to handle extension parameters on types
• Implements workarounds for compiler-generated types that inherit attributes from extension members

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/tools/illink/test/Mono.Linker.Tests/TestCasesRunner/ResultChecker.cs	Adds workaround to skip attribute validation for compiler-generated extension member types
src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/ExtensionsDataFlow.cs	New test case for traditional extension method data flow analysis
src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/ExtensionMembersDataFlow.cs	New test case for C# 14 extension members data flow analysis
src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/DataFlowTests.cs	Adds test methods for the new extension data flow test cases
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/TrimAnalysisVisitor.cs	Updates parameter handling to support extension parameters on types
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/ParameterProxy.cs	Enhances parameter proxy to handle extension parameters with proper indexing
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/MethodParameterValue.cs	Removes obsolete constructors for method parameter values
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/FlowAnnotations.cs	Updates parameter annotation retrieval for extension methods
src/tools/illink/src/ILLink.RoslynAnalyzer/IMethodSymbolExtensions.cs	Adds extension parameter detection and parameter counting logic
src/tools/illink/src/ILLink.RoslynAnalyzer/ILLink.RoslynAnalyzer.csproj	Reorders NoWarn directives and removes conditional compilation warning suppression
src/tools/illink/src/ILLink.RoslynAnalyzer/DataFlow/LocalDataFlowVisitor.cs	Updates method and property call handling for extension parameters
src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/ResultChecker.cs	Duplicates the compiler-generated type workaround for NativeAOT testing
eng/Versions.props	Updates Microsoft.CodeAnalysis version from 4.8.0 to 4.14.0

[jtschuster]

Thank you!