Hide Audit comment table reads behind an API
Summary: Ref T4896. Buries all direct access to the table so we can limit the surface area affected by the migration.
Test Plan:
- Grepped for PhabricatorAuditComment.
- Grepped for audit_comment.
- Viewed a bunch of comments.
- Added a comment.
- Reindexed a commit.
- Searched for unique term in new comment.
Reviewers: btrahan, joshuaspence
Reviewed By: joshuaspence
Subscribers: epriestley
Maniphest Tasks: T4896
Differential Revision: https://secure.phabricator.com/D10019