[clang] [Clang] Reapply CWG2369 "Ordering between constraints and substitution" (PR #122423)

[via cfe-commits]

cor3ntin wrote:

@alexfh It wouldn't fix your issue, see this comment https://github.com/llvm/llvm-project/pull/122423#issuecomment-2585390531 (there were 2 issues, a bug in the PR implementation, and an unfortunate breakage caused by some libraries relying on non-conforming behavior)

https://github.com/llvm/llvm-project/pull/122423