[llvm] [Code Coverage] Add a tool to check test coverage of a patch (PR #71841)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> I know we are not doing this right now, but I wonder if we should have tests for python scripts as well so that we can run it with our supported python version and see if it works, because it can be hard to spot in a review.

I am very much in favor of starting to add tests for these utilities. I wouldn't block this patch on having tests, but it's definitely a good practice in general. It's on my todo list to get tests up and running for `git-clang-format`.

https://github.com/llvm/llvm-project/pull/71841