run `git clang-format` to suggest changes on diff

`git-clang-format` will suggest changes on diff lines, rather than on
the whole file

the last block prints the diff so contributors can apply it to their
code locally
1 job for !960 with clang-format-gitlab-ci in 1 minute and 4 seconds (queued for 5 minutes and 17 seconds)
Status Name Job ID Coverage
passed clang_format #118570