Rename PhabricatorPolicyRule subclasses for consistency
Summary: Ref T5655. Fixes T6849. This is another take on D11131, which was missing the DB migration and was reverted in rP7c4de0f6be77ddaea593e1f41ae27211ec179a55.
Test Plan: Ran ./bin/storage upgrade and verified that the classes were renamed in the phabricator_policy.policy table.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D11166