Add new DiagnosticMethodInfo public API

[MichalStrehovsky]

This add support for the new public API for all runtime flavors and switches Tasks logging to use it (we could make it a separate PR, I don't mind either way). Switching tasks logging to the new API saves 1.1% in size on webapiaot because the compiler no longer needs to consider all delegates targets of reflection.

TODO:

• Feature switch to disable this outside native AOT so that <StackTraceSupport>false</StackTraceSupport> really means this doesn't work.
• Trimming test with the feature switch disabled
• Native AOT smoke test to exercise some of the "don't have reflection metadata" paths. libraries tests always have reflection metadata for everything.
• Maybe also use this in BCL instead of get_Method.
• Finish the feature switch (add ILLink XML)

#96528

[dotnet-issue-labeler]

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[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

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[MichalStrehovsky]

This could alternatively be this, but not sure how important that is:

Suggested change

	DiagnosticMethodInfo? dmi = DiagnosticMethodInfo.Create(@delegate);
	return dmi?.Name ?? "<unknown>";
	if (StackTrace.IsSupported)
	{
	DiagnosticMethodInfo? dmi = DiagnosticMethodInfo.Create(@delegate);
	return dmi!.Name;
	}
	else
	{
	return @delegate.Method.Name;
	}

[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

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Azure Pipelines successfully started running 1 pipeline(s).

[MichalStrehovsky]

1.1% size savings on webapiaot! MichalStrehovsky/rt-sz#29 (comment)

[MichalStrehovsky]

This is ready for review, cc @dotnet/ilc-contrib

[jkotas]

Is this measurably more expensive than the existing code on regular CoreCLR?

[MichalStrehovsky]

On regular coreclr there's the one extra allocation but otherwise I don't expect impact. DiagnosticMethodInfo just wraps the underlying MethodInfo.

On native AOT we unnecessarily materialize type name and class name. I thought about structuring DiagnosticMethodInfo so that it wraps MetadataReader and a bunch of handles but ended up not doing it because we'd still need strings for the open method delegate cases (or somehow wrestle metadata handles out of reflection objects in that case).

[jkotas]

LGTM!