JIT: Remove _MAYBENULL Helper uses

[adamperlin]

Resolves#132343 and resolves#132185; Remove requests for _MAYBENULL helper variants in the JIT for TypeHandle -> RuntimeType{Handle} conversions.

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[Copilot]

Pull request overview

This PR updates the CoreCLR JIT to stop requesting the *_MAYBENULL helper variants for TypeHandle → RuntimeType{Handle} conversions, instead using explicit null checks where needed and the non-_MAYBENULL helpers otherwise.

Changes:

• CEE_REFANYTYPE import now emits an inline handle != 0 conditional that either returns default(RuntimeTypeHandle) or calls CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPEHANDLE.
• Type.GetTypeFromHandle intrinsic folding no longer rewrites to CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE_MAYBENULL; it assumes the non-null helper flow and rewrites to CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE.

Reviewed changes

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File	Description
src/coreclr/jit/importercalls.cpp	Simplifies Type.GetTypeFromHandle intrinsic rewriting to always use the non-_MAYBENULLCORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPE helper when the argument is a TypeHandle→RuntimeTypeHandle helper call.
src/coreclr/jit/importer.cpp	Replaces CORINFO_HELP_TYPEHANDLE_TO_RUNTIMETYPEHANDLE_MAYBENULL usage in CEE_REFANYTYPE with an explicit null check and conditional default initialization.

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Pull request overview

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

[EgorBo]

Should this PR physically remove _MAYBENULL everywhere?

[adamperlin]

Should this PR physically remove _MAYBENULL everywhere?

It's still used in the interpreter, so I thought maybe removing it in the interpreter could be a separate change? I'm happy to add that to this PR though!

[jkotas]

I think it would be nice to do it all on one PR