[clang] [clang-tools-extra] [clang-tidy][dataflow] Add `bugprone-null-check-after-dereference` check (PR #84166)

[via cfe-commits]

Discookie wrote:

Should be ready for another round of review.

Simplified a lot of the logic, implemented most of the changes requested, added support for `p != nullptr`, and `void f(int **ptr)` invalidating the value of `*ptr`.

I've been experimenting with trying to remove `TK_IgnoreUnlessSpelledInSource`, without much luck. I need to be able to set a new `Value` to all of my pointers, and currently the framework doesn't let me set it in a persistent manner.
I'm still yet to refactor handling `Top`, currently it's used in early returns where possible, but I still need to think of a clear way to make central functions for it.


https://github.com/llvm/llvm-project/pull/84166