[clang] [Clang] Clarify diagnostic notes for implicitly generated deduction guides (PR #96084)

[via cfe-commits]

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

Two nits, but the rest seems reasonable. I agree that `make_scope_exit` is probably the only sane way of doing this here.

While I still maintain that the formatting of this could be better, I also agree that this is a problem that we’ll probably have to solve separately.

https://github.com/llvm/llvm-project/pull/96084