[clang-tools-extra] Add bugprone-loop-variable-copied-then-modified clang-tidy check. (PR #157213)

[Julia Hansbrough via cfe-commits]

flowerhack wrote:

Thanks for the feedback; I believe I've addressed all comments, save one comment from @zwuis which I requested clarification on.  Let me know if there's anything else.

https://github.com/llvm/llvm-project/pull/157213