R1:e5fe4dffe1dc

Add a "Published document changed" rule to Herald for Phriction documents

Summary: Depends on D20519. Ref T13283. See PHI1202. Add a new rule which triggers when the current/most-recent transaction group includes a "content" or "publish" transaction, which means the published document content has changed.

Test Plan:
- Wrote a Herald rule using this field.
- Created a document (rule matched).
- Edited a document (rule matched).
- Edited a document, saving as a draft (no match).
- Edited a draft…