Add trimming intrinsic for EventInfo.EventHandlerType.GetMethod("Invoke")

[sbomer]

Fixes#114113

Because ILLink and ILC keep the Invoke method on delegates, there shouldn't be a warning for the common pattern of EventInfo.EventHandlerType.GetMethod("Invoke").

It's possible to break this logic by using a custom EventInfo - see the testcase and discussion in the original issue.

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[Copilot]

Pull Request Overview

This PR prevents spurious trimming warnings when calling EventInfo.EventHandlerType.GetMethod("Invoke") on delegates by adding special-case handling in the dataflow logic, and adds a test covering both delegate and custom-EventInfo scenarios.

• Added a new test case EventHanderTypeGetInvokeMethod to cover the delegate and non-delegate paths.
• Updated HandleCallAction to recognize and allow Invoke on delegate types without additional requirements.
• Refactored several MethodReturnValue implementations to carry both the original method proxy and its definition.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/EventHanderTypeGetInvokeMethod.cs	New test exercising delegate and custom EventInfo Invoke scenarios
src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/ReflectionTests.cs	Registered new analyzer test for the above case
src/tools/illink/src/linker/Linker.Dataflow/MethodReturnValue.cs	Switched to carrying a MethodProxy and a MethodDefinition
src/tools/illink/src/ILLink.Shared/TrimAnalysis/MethodReturnValue.cs	Added Method property to shared trim analysis value
src/tools/illink/src/ILLink.Shared/TrimAnalysis/HandleCallAction.cs	Special-case logic for GetMethod("Invoke") on delegates
src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/MethodReturnValue.cs	Updated Roslyn analyzer to construct MethodProxy
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/MethodReturnValue.cs	Updated AOT dataflow to construct MethodProxy and separate MethodDesc

Comments suppressed due to low confidence (5)

src/tools/illink/src/linker/Linker.Dataflow/MethodReturnValue.cs:34

• The constructor assigns to Method but no Method field or property is declared in this class. Add a public readonly MethodProxy Method; (or auto-property) to match the assignment and avoid a compile error.

 Method = method;

src/tools/illink/src/ILLink.RoslynAnalyzer/TrimAnalysis/MethodReturnValue.cs:25

• This line assigns to Method but the class does not declare a Method field or property. Introduce a public MethodProxy Method { get; } to store the proxy and ensure the code compiles.

 Method = new MethodProxy (methodSymbol);

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/MethodReturnValue.cs:26

• The constructor sets Method but no such member exists. Add a public MethodProxy Method { get; } or similar declaration so the code compiles and can supply the proxy where needed.

 Method = new MethodProxy(method);

src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/EventHanderTypeGetInvokeMethod.cs:14

• [nitpick] The class name EventHanderTypeGetInvokeMethod is missing an 'l' in Handler. Consider renaming to EventHandlerTypeGetInvokeMethod for clarity and consistency.

	public class EventHanderTypeGetInvokeMethod

src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/ReflectionTests.cs:38

• [nitpick] The test method name EventHanderTypeGetInvokeMethod is missing an 'l' in Handler. Update it to EventHandlerTypeGetInvokeMethod to match the corrected class name.

 public Task EventHanderTypeGetInvokeMethod ()

[jtschuster]

LGTM, thank you!