Support HasThis and ExplicitThis calling conventions in AssemblyBuilder and DynamicMethod

[steveharter]

Fixes issues around using calli with CallingConventions.HasThis and CallingConventions.ExplicitThis both when generating the IL and when executing the IL.

Fixes #113626

[Copilot]

Pull Request Overview

This PR adds support for the HasThis calling convention in PersistedAssemblyBuilder by extending the signature calling convention and updating associated tests and module builder logic.

• Introduces an extended enum (SignatureCallingConventionEx) with a HasThis flag.
• Adds a new test (AssemblyWithInstanceBasedFunctionPointer) to verify the instance-based function pointer behavior.
• Updates ModuleBuilderImpl to check and set the HasThis flag based on the calling convention.

Reviewed Changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Reflection.Emit/src/System/Reflection/Emit/SignatureCallingConventionEx.cs	Adds an extended enum for calling convention flags.
src/libraries/System.Reflection.Emit/tests/PersistedAssemblyBuilder/AssemblySaveAssemblyBuilderTests.cs	Adds tests for instance-based function pointer calls.
src/libraries/System.Reflection.Emit/src/System/Reflection/Emit/ModuleBuilderImpl.cs	Updates GetSignatureConvention to incorporate the HasThis flag.

Files not reviewed (2)

• src/libraries/System.Reflection.Emit/src/System.Reflection.Emit.csproj: Language not supported
• src/libraries/System.Reflection.Emit/tests/System.Reflection.Emit.Tests.csproj: Language not supported

Comments suppressed due to low confidence (1)

src/libraries/System.Reflection.Emit/tests/PersistedAssemblyBuilder/AssemblySaveAssemblyBuilderTests.cs:351

• [nitpick] Consider adding a comment to clarify why a static method is being used, how it simulates an instance call with HasThis, and what the expected behavior is, to aid future maintainers in understanding the test.

il.EmitCalli(OpCodes.Calli, CallingConventions.HasThis, typeof(Guid), null, null);

[Copilot]

Ensure that the conversion from SignatureCallingConvention to SignatureCallingConventionEx preserves all intended flags without conflicts. Adding a short comment to document why the cast to the extended enum is safe would improve maintainability.

[steveharter]

Wasm build failures due to #113685

[AaronRobinsonMSFT]

/cc @dotnet/jit-contrib

[jkotas]

Use 'object' for type in tests

What was wrong with MyClassWithGuidProperty?

[steveharter]

What was wrong with MyClassWithGuidProperty?

Nothing, just wanted to make sure I can use object for reference types and that the concrete type wasn't necessary. It was verifying there are no issues for shared generated IL across different reference types. I'll add a comment about this.

[pentp]

Could simplify the condition to (callingConvention & (CallingConventions.HasThis | CallingConventions.ExplicitThis)) == CallingConventions.HasThis