[clang] [Clang][C++23] Implement P2448R2: Relaxing some constexpr restrictions (PR #77753)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

Okay then, could you please review or give me an LGTM if everything is ok? The patch transformed a bit since it was first approved. It doesn't enable feature as extension now, it incorporates changes and test highlighted by https://github.com/llvm/llvm-project/pull/77753#issuecomment-1899137960 and I renamed diagnostic messages according to other similar ones.

https://github.com/llvm/llvm-project/pull/77753