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

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I'll have to take another look at this when I get more time for it, but I'm glad this is getting further attention.  I'd refactored this only a year or two ago (preivously it was a single really long function with a loop), so it is disappointing that we're needing to refactor it again already.  

Collection of these arguments is unfortunately quite a task and ends up being a bit of trial/error, so hopefully the previous version ends up providing enough tests/etc to help inform this one.

That said, I'd vastly prefer this patch get split up into a few.  The straight refactor + new visitor, plus it seems like there are a handful of similar/related refactors that are happening here too.

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