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