Add an `$args` parameter to `comment_text` and `get_comment_text` filters. Adds filter docs. Improve docblocks for `get_comment_text()` and `comment_text()`.

Props simonwheatley, ericlewis, DrewAPicture.
Fixes #14856. 



git-svn-id: https://develop.svn.wordpress.org/trunk@25555 602fd350-edb4-49c9-b593-d223f7449a82