As CommentFormatter no longer needs HTMLFormatter, remove
the inheritance and make addReplyLinks a static method.
Testing locally this is marginally slower, going from 2.55s
to 2.9s for the CommentFormatterTest case.
Bug: T266317
Bug: T267973
Change-Id: If69749cae678a1647a138d782a32032189f55cec
I haven't really reviewed the outputs, but at least a) they don't
crash b) they will fail if the output suddenly changes (which could
cause problems due to caching).
Bug: T252555
Change-Id: I1bbcbc5dd17ce1e24b3622062f5e8df4baf5f389