[clang] [Clang] Implement P2280R4 Using unknown pointers and references in constant expressions (PR #95474)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

We have a new crash on new code introduced since I last worked on this, I am guessing it just requires some additional checks.

https://github.com/llvm/llvm-project/pull/95474