[clang] [clang-tools-extra] Reapply "[Clang] Unify interface for accessing template arguments as written for class/variable template specializations (#81642)" (PR #91393)

[Erich Keane via cfe-commits]

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

I have no problem with this, if it passes CI, I think this is fine.

https://github.com/llvm/llvm-project/pull/91393