Modularize all Herald pre-commit ref fields
Summary: Ref T8726. Just (pre-commit content) one more left.
Test Plan:
- Created a big rule with every field.
- Migrated it.
- Verified the rule was still the same.
- Pushed a bunch of changes and reviewed the transcripts.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T8726
Differential Revision: https://secure.phabricator.com/D13600