[libcxx-commits] [libcxx] [libcxx][docs] Make test name pattern documentation more obvious (PR #73136)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne approved this pull request.

LGTM w/ comments. It would be nice to move the rest of the documentation for the test format to `.rst` too, otherwise we'll have things in multiple places which means more likely to forget to update new information everywhere.

https://github.com/llvm/llvm-project/pull/73136