R1:b3e196b69400

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

Maniphest Tasks: T6849, T5655…