Rename PHIDType classes
Summary: Ref T5655. Rename PhabricatorPHIDType subclasses for clarity (see discussion in D9839). I'm not too keen on some of the resulting class names, so feel free to suggest alternatives.
Test Plan: Ran unit tests.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin, hach-que
Maniphest Tasks: T5655
Differential Revision: https://secure.phabricator.com/D9986