[clang] [clang] Prefer exact template-template matches in partial ordering (PR #216113)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

`SemaTemplate` is indeed a good place to put the test. Generally `SemaCXX` is never a wrong place for a C++ test, even if I personally wish it was less of a dumping ground.

https://github.com/llvm/llvm-project/pull/216113