Handling IL-level .override corner cases

[MichalStrehovsky]

The managed type system doesn't seem to handle various corner case behaviors around .override in IL. See tests blocked on this issue.

Putting this under native AOT, but it's in the shared managed type system.

Possibly related to the following TODO:

runtime/src/coreclr/tools/Common/TypeSystem/Common/MetadataVirtualMethodAlgorithm.cs

Lines 468 to 470 in 7693b6d

	// We should check to see if a the DefiningMethod on the base unification group is overridden via MethodImpl
	// TODO! check to see if we need to check for MethodImpls affecting other members of the unification group
	// other than the defining method

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