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

[Kim Gräsman via cfe-commits]

kimgr wrote:

@sdkrystian Thank you! I think there's some more subtleties to it, but I don't really have my head around it yet. I'll first try to understand what we're trying to achieve and then ping back of I need help with something concrete.

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