[clang] [NFC][analyzer] Improve tracking of the current Block & LocCtx (PR #185107)

[Balázs Benics via cfe-commits]

steakhal wrote:

I'd propose merging this as it's reviewed.

> I know that this PR is already big, but I feel that completing step 1. of this roadmap would be a natural "completed" state for it. Moreover, I expect that downstream projects might want to temporarily revert these changes if they want to postpone the resolution of merge conflicts -- and many small commits would make that (more) troublesome.

This seems hypothetical. I'd not put constraints on our way of working without evidence.

https://github.com/llvm/llvm-project/pull/185107