[clang] [Clang][Sema] Ignore previous partial specializations of member class templates explicitly specialized for a implicitly instantiated class template specialization (PR #113464)

[Matheus Izvekov via cfe-commits]

https://github.com/mizvekov commented:

Sorry for the late review. The patch looks fine, thanks!

I have a minor concern about the 3x repetition here, and would be happy to see this refactored at some point. 

https://github.com/llvm/llvm-project/pull/113464