Make stored custom fields work with v3 EditEngine API

Summary: Ref T11114. This makes the unusual stored custom fields ("Blame Rev", "Revert Plan", etc) work somewhat correctly (?) with EditEngine.

Test Plan:

• Created, updated and edited revisions with unusual stored custom fields like "Blame Rev".
• Observed that these fields now populate in "differential.revision.edit" when available.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11114

Differential Revision: https://secure.phabricator.com/D17068