[clang] [Clang] Unify interface for accessing template arguments as written for class/variable template specializations (PR #81642)

[Erich Keane via cfe-commits]

erichkeane wrote:

>The "most breaking" change is to AST Matchers, insofar that hasTypeLoc will no longer match class template specializations (since they no longer store the type as written). I wasn't entirely sure what to replace the tests for this behavior with, so I just commented them out... guidance/feedback would be appreciated on this.

This part has implications that I'm not sure about, and likely needs to A: be in the 'breaking changes' doc, and B: Have Aaron comment on it.

https://github.com/llvm/llvm-project/pull/81642