[clang] [Clang][Sema] Reject template arguments not equivalent to their copies (part of P2308R1) (PR #193754)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

I don't have any other concerns, and the tests seem right, but it is a little subtle.  I'd like someone else on the list to OK it as well.

https://github.com/llvm/llvm-project/pull/193754