Ref T11114. This creates differential.revision.edit (a modern, v3 API method) and redefines the existing methods in terms of it.

Both differential.createrevision and differential.updaterevision are now internally implemented by building a differential.revision.edit API call and then executing it.

I think this covers everything except custom fields, which need some tweaking to work with EditEngine. I'll clean that up in the next change.

• Created, updated, and edited revisions via arc.
• Called APIs manually via test console.
• Stored custom fields ("Blame Rev", "Revert Plan") aren't exposed yet.