[clang-tools-extra] [clang-tidy] Implement alphabetical order test (PR #166072)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> The intent is to surface duplicates so developers can merge them manually. However, when run with the --fix flag, the tool deletes the later duplicate entry outright, leaving the file as:

Could we make the script do nothing and don't delete duplicated entries? Just sort them in alphabetical order and let the user fix it by hand.

https://github.com/llvm/llvm-project/pull/166072