Share portions of CoreCLR and Mono CoreLib's ILLinkTrim.xml file

[eerhardt]

This reduces the duplication between these libraries, and allows for easier maintenance going forward.

Fix #37255

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[marek-safar]

Is .Shared suffix necessary?

[eerhardt]

It technically isn't necessary, but since ILLink.Descriptors.xml is the full name of the resource embedded in the assembly, I thought it would be confusing to someone who thought this was the full descriptor file. Putting Shared in the file name qualifies it being the "shared" pieces, and not the full file.

[marek-safar]

ok

[marek-safar]

Could you also rename the file to ILLink.Descriptors.xml ?

[eerhardt]

I was going to do that as part of #37651.

[stephentoub]

Separate from this PR, if this is only used by tests, can it be part of _LibraryBuild file instead?

[eerhardt]

I looked at this yesterday,

runtime/src/libraries/Common/src/Interop/Interop.ICU.cs

Lines 27 to 28 in a9626b9

	[DllImport(Libraries.GlobalizationNative, EntryPoint = "GlobalizationNative_GetICUVersion")]
	internal static extern int GetICUVersion();

I was thinking of just moving the P/Invoke to the tests.

But now that I look again, our Globalization.Native shim is replaced with QCall -- can you do that from an assembly outside of S.P.Corelib?

If not, then yes it could be moved to _LibraryBuild.

[jkotas]

QCalls are for CoreLib-only.