Fix few startup path issues with interpreter

[janvorli]

This change fixes the following issues:

• Reverse pinvoke to method marked by UnmanagedCallersOnly attribute. The InterpExecMethod is entered in GC preemptive mode in that case, but it is expected to run in GC cooperative mode.
• Pinvoke to method marked by SuppressGCTransition attribute . The pinvoke is entered in GC preemtive mode, but it needs to be called in GC cooperative mode.
• Calling a delegate or a similar case when IL stub is used. The interpreter code is set only on the IL stub MethodDesc, but it needs to be set on both the IL stub and the original MethodDesc.

[Copilot]

Pull Request Overview

This PR fixes three interpreter-related startup path issues in the CoreCLR runtime related to GC mode transitions and method descriptor setup:

• Fixes reverse pinvoke methods with UnmanagedCallersOnly attribute to run in GC cooperative mode instead of preemptive mode
• Ensures pinvoke methods with SuppressGCTransition attribute are called in GC cooperative mode
• Sets interpreter code on both IL stub and original MethodDesc when using delegates or similar IL stub scenarios

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/coreclr/vm/prestub.cpp	Adds interpreter code setting for both current and config MethodDesc, and implements GC mode transition for UnmanagedCallersOnly methods
src/coreclr/vm/interpexec.cpp	Adds conditional GC cooperative mode transition for methods with SuppressGCTransition attribute

Comments suppressed due to low confidence (1)

src/coreclr/vm/interpexec.cpp:1881

• This closing brace appears to be misplaced. It should close the GCX_MAYBE_COOP block, but the indentation and structure suggest it's closing the wrong scope. The GCX_MAYBE_COOP block on line 1878 should have its closing brace aligned with its opening.

                    }

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[davidwrighton]

This looks good to me now.