[clang] [clang-tools-extra] [clang] Implement CWG2398 provisional TTP matching to class templates (PR #94981)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I've not done as in depth of a review as Corentin, but I approve of the direction here, I think the approach is correct, and most of the changes are fairly mechanical.  So once Corentin is happy with the changes, so am I.

https://github.com/llvm/llvm-project/pull/94981