Add IDynamicInterfaceCastable interface

[elinor-fung]

Approved API: #36654

• Add IDynamicInterfaceCastable and DynamicInterfaceCastableImplementation
• IDynamicInterfaceCastable.GetInterfaceImplementation is called as a fallback for isinst, castclass, and interface dispatch when casting in the normal way fails.
• Add tests

cc @AaronRobinsonMSFT @jkoritzinsky

[Dotnet-GitSync-Bot]

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[benaadams]

Does RuntimeHelpers.CoreCLR.cs also need to change?

runtime/src/coreclr/src/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs

Lines 345 to 349 in 00c0328

	// Types that require non-trivial interface cast have this bit set in the category
	private const uint enum_flag_NonTrivialInterfaceCast = 0x00080000 // enum_flag_Category_Array
	| 0x40000000 // enum_flag_ComObject
	| 0x00400000;// enum_flag_ICastable;

[elinor-fung]

Yes - that is changed: https://github.com/dotnet/runtime/pull/37042/files#diff-62699d7b49d1d40e84362b31c5df4db4R343

[AaronRobinsonMSFT]

/cc @davidwrighton @MichalStrehovsky