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

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@mstorsjo I think you can revert both -- @mizvekov's patch could get rid of this reliance in some other way.

https://github.com/llvm/llvm-project/pull/111173