[clang-tools-extra] [clang-tidy] treat fragment includes as main-file parts (PR #180282)

[via cfe-commits]

https://github.com/zeyi2 commented:

Sorry that I could only do a quick review this time due to my availability. Overall the `clang-tidy` part looks good, but I need more time to fully review the implementation. 

Please see the inline comments below, and please resolve the conflicts in `ReleaseNotes.rst` :)

https://github.com/llvm/llvm-project/pull/180282