R1:b373dcef7448

Restore some minor state behaviors to Differential on EditEngine

Summary:
Ref T11114. This restores:

- Commandeering should exeucte Herald.
- Commandeering should swap reviewers.
- "Request Review" on an "Accepted" revision should downgrade reviewers so they have to accept again.

Test Plan:
- Commandeered, saw Herald run and reviewers swap.
- Requested review of an accepted revision, saw it drop down to "Needs Review" with "Accepted Prior" on the reviewer.

Reviewers: chad

Reviewed By: chad…