[clang] [Clang][Sema] Diagnose class member access expressions naming non-existent members of the current instantiation prior to instantiation in the absence of dependent base classes (PR #84050)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

`Sema.h` changes look good to me.

https://github.com/llvm/llvm-project/pull/84050