[clang] [llvm] [clang-format] Add CI check confirming ClangFormatStyleOptions.rst is up-to-date. (PR #111513)

[Iuri Chaer via cfe-commits]

ichaer wrote:

> The documentation build workflow is not really the correct place to put this.

Yeah, I agree, but I couldn't find a place which looked correct :sweat_smile:. This thing of adding built artifacts to the repo always introduces sadness... the documentation build workflow looked like the least bad place. I'll gladly take input on this!

> Also, why can't we just run the python script as part of building the docs instead of committing the result of the script to the repository?

That's an excellent question, maybe @owenca will know! I should have asked in https://github.com/llvm/llvm-project/pull/96804#discussion_r1718407404; what I did instead was try to reason out an explanation based on what I could see, and I came up with two theories. The first one is that we want for `ClangFormatStyleOptions.rst` to be available to anyone browsing the repo... it's not very convincing, but it doesn't sound absurd. I could definitely get behind my second theory, though: we want to force everyone to review `ClangFormatStyleOptions.rst` before merging changes to the header files from which it is produced, and putting it in the repo is a good way to inject that into the code review process.

Anyhow, I'm proposing this because in https://github.com/llvm/llvm-project/pull/96804#discussion_r1718407404 I thought that it was an unreasonable burden for project maintainers having to manually gate on changes which may affect `ClangFormatStyleOptions.rst`, and also an unnecessary source of friction during code reviews, so I volunteered to automate that part.

https://github.com/llvm/llvm-project/pull/111513