[clang] Reapply "[Clang][Sema] Refactor collection of multi-level template argument lists (#106585, #111173)" (PR #111852)

[Krystian Stasiowski via cfe-commits]

sdkrystian wrote:

@ilya-biryukov This is caused by the change to `CheckFunctionTemplateSpecialization` in `SemaTemplate.cpp`; we previously called `DeduceTemplateArguments` with the canonical declaration of the primary template, but now we call it with the passed in primary template declaration. Since lookup typically finds the most recent visible declaration, the primary template used for the explicit specialization is `#2`.

https://github.com/llvm/llvm-project/pull/111852