[mono][interp] Sign extend I4 return value since jit-ed code expects it

[BrzVlad]

Fixes #115859

[Copilot]

Pull Request Overview

This PR ensures that 32-bit integer return values from interpreted methods on amd64 are sign-extended to match JIT expectations and updates the call-result widening logic to include the interpreter backend alongside LLVM.

• Sign-extend I4 return values in the amd64 interpreter call context.
• Extend mono_emit_widen_call_res to treat the interpreter path similarly to LLVM for return-value widening.

Reviewed Changes

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

File	Description
src/mono/mono/mini/mini-amd64.c	Sign-extend I4 return value on the amd64 interpreter path when returning in RAX.
src/mono/mono/mini/method-to-ir.c	Rename and extend the “might_use_llvm” flag to also cover the interpreter path.

Comments suppressed due to low confidence (2)

src/mono/mono/mini/method-to-ir.c:2238

• Update this comment to mention that widening now applies for both LLVM and the interpreter backends, not just LLVM.

		// LLVM code doesn't uses zero extend the full word while jit expects it.

src/mono/mono/mini/mini-amd64.c:1480

• Add a unit test for the interpreter on amd64 to verify that negative I4 return values are correctly sign-extended when placed in RAX.

		if (sig->ret->type == MONO_TYPE_I4 && ainfo->storage == ArgInIReg && ainfo->reg == AMD64_RAX)

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[lateralusX]

LGTM!

[BrzVlad]

Replaced by #117336