Rename PhutilRemarkupRule subclasses
Summary: Ref T5655. Some discussion in D9839. Generally speaking, Phutil{$name}RemarkupRule is clearer than PhutilRemarkupRule{$name}.
Test Plan: Not yet tested... this is likely to break external code, so I'm not sure whether or not we want to pursue this.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Maniphest Tasks: T5655
Differential Revision: https://secure.phabricator.com/D9993