[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)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Quite a bit of cleanup level stuff, plus wanting 1 minor refactor here (re the lookup function), but otherwise is pretty good.

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