Modernize all Herald DifferentialDiff fields

Summary: Ref T8726. This deals with all the Differential diff fields, same deal as previous changes.

Test Plan:

• Wrote a rule with every field.
• Migrated it.
• Saw the same rule working.
• Rigged the hell out of transcripts (diffs normally do not generate transcripts, because the only action is "block" and they don't exist yet when Herald runs).
• Verified that all fields looked sensible in the transcript.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8726

Differential Revision: https://secure.phabricator.com/D13590