Fix for issue 5343: Assert Failure: !"Cannot take the address of an uninstantiated...

Fix for issue 5343: Assert Failure: !"Cannot take the address of an uninstantiated generic method." (dotnet/coreclr#5347)

The problem was that the delegates code base was not correctly instantiating interface GVMs on target types
(after finding the target method on the target type using slot numbers), and ended up calling uninstantiated
generic method definitions on delegate invokes.

Commit migrated from https://github.com/dotnet/coreclr/commit/c1cf38369531d9fb98a1b26166a1e48c0c8c808d