[clang] [clang] [Sema] Add assertion about expected type classes when building MemberPointerType (PR #119105)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

(This was meant as a follow-up to https://github.com/llvm/llvm-project/pull/118236 to add the assertion discussed in [this comment](https://github.com/llvm/llvm-project/pull/118236#discussion_r1865179512), but I'm not proceeding with it because the assertion is tripped in more cases than hypothesized.)

https://github.com/llvm/llvm-project/pull/119105