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

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

Ah, I never got around to pushing the reverts earlier. Do you think you'll have a fix within a couple of hours, or should we just go ahead with the revert and do a clean reland later, once this issue is sorted out (and you've checked that Qt actually does compile still - there seems to be many issues in this area in that file).

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