[clang] [Clang] Improve diagnostics to show the correct position for `[[maybe_unused]]` before a using-alias (PR #223910)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 approved this pull request.

Please also add a release note, otherwise LGTM. thanks!

https://github.com/llvm/llvm-project/pull/223910