[clang] [clang-format] Add test to ensure formatting options docs are updated (PR #118154)

[Aiden Grossman via cfe-commits]

boomanaiden154 wrote:

> Hm, or it's not related to the testcase, but it happens every time we build now due to https://github.com/llvm/llvm-project/commit/6bec1806c9cc90f6e72fc04698f4221c86c5f95e

That's more likely to be due to #111513. That got reverted. If it's still an issue here, let me know. Everything should be read only here, but that doesn't mean things aren't getting opened with inappropriate permissions.

https://github.com/llvm/llvm-project/pull/118154