[clang-tools-extra] [llvm] [clang][clang-doc] Add basic e2e test to clang-doc (PR #93928)

[Paul Kirth via cfe-commits]

ilovepi wrote:

Also, I just noticed that the first comment has an `@` in it. The first comment in Github is special, as its really the body of the commit message, and will become that when you hit `Squash and merge`. Your question for @petrhosek may not even have been sent, as I don't know how github handles that. Please update the first message to be appropriate for the commit body, and copy any questions/context you have to another comment.

https://github.com/llvm/llvm-project/pull/93928