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

[Julia Hansbrough via cfe-commits]

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+// RUN: %check_clang_tidy -std=c++17-or-later %s bugprone-loop-variable-copied-then-modified %t
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flowerhack wrote:

C++17 has class template argument deduction, and I thought it'd be a useful test case to see if the FixIt does the correct thing in that case.  I can change that or put that case in a separate file, though, if you'd prefer?  Just let me know.

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