Add some tests for subclasses

Summary: Add some tests to ensure that ArcanistXHPASTLinterRule subclasses are properly implemented. This should catch issues such as two linter rules having the same ID value. See D13272 for a similar change.

Test Plan: arc unit

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D13274