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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

FYI https://github.com/itanium-cxx-abi/cxx-abi/issues/184 is the tracking issue for the mangling rules we need here.
We will probably end up with something quite different than what I coded here so far.

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