illink: TypeMapAssociation attribute always trimmed if there's a TypeMap attribute for the same type.

[rolfbjarne]

Test case:

[assembly: TypeMap<UsedExternalTypeMap>("BothInExternalAndProxy", typeof(BothInExternalAndProxy), typeof(BothInExternalAndProxy))]
[assembly: TypeMapAssociation<UsedExternalTypeMap>(typeof(BothInExternalAndProxy), typeof(BothInExternalAndProxyTarget))]

class BothInExternalAndProxy;
class BothInExternalAndProxyTarget;

Console.WriteLine(new BothInExternalAndProxy());

results in the TypeMapAssociation attribute being trimmed away.

This happens because when illink sees a TypeMap attribute, it marks the target type as instantiated:

runtime/src/tools/illink/src/linker/Linker/TypeMapHandler.cs

Line 111 in cab811a

_context.Annotations.MarkInstantiated(targetTypeDef);

which causes MarkRequirementsForInstantiatedTypes to exit early:

runtime/src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

Lines 3511 to 3514 in cab811a

	protected virtual void MarkRequirementsForInstantiatedTypes(TypeDefinition type)
	{
	if (Annotations.IsInstantiated(type))
	return;

and then TypeMapHandler.ProcessInstantiatedType later in the method isn't called:

runtime/src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

Line 3532 in cab811a

_typeMapHandler.ProcessInstantiated(type);

so then the TypeMapAssociation attribute is never marked.

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[rolfbjarne]

CC @simonrozsival in case you run into this too with Android