Modularize all DifferentialRevision fields
Summary: Ref T8726. Make all the DifferentialRevision stuff modular.
- Created a rule with all fields.
- Ran upgrade.
- Saw all fields preserved with new modular versions.
- Used test console to run rule with all fields, verified field values as broadly sensible.
Reviewed By: btrahan
Maniphest Tasks: T8726
Differential Revision: https://secure.phabricator.com/D13598