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

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https://github.com/Discookie commented:

Thanks for the reviews! Fixed a lot of the comments, and I have a few more things to test for the rest.

@gribozavr Thank you for the thorough introduction to your approaches, and the links to related works as well! Templated types are something I didn't take a look at before, will need to experiment with those as well.

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