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

[Owen Pan via cfe-commits]

owenca wrote:

> 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?

Because only part of the doc is generated by `dump_format_style.py`. See https://github.com/llvm/llvm-project/blob/1809d0fa1c15b16ca94381d8be3ef70c4a83c36b/clang/docs/ClangFormatStyleOptions.rst?plain=1#L3.

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