[clang] [Clang][Sema] Refactor collection of multi-level template argument lists (PR #106585)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@sdkrystian do you plan to reland this patch in some other form these days? I'm going to restart my cwg 2369 work on top of it.

https://github.com/llvm/llvm-project/pull/106585