Replace Differential Edit controller with EditEngine-driven EditPro controller

Summary:
Ref T11114. This replaces the old edit controller with a new one based entirely on EditEngine.

This removes the CustomFieldEditEngineExtension hack for Differential, since remaining field types are fairly straightforward and work with existing EditEngine support, as far as I can tell.

Test Plan:
  - Created a revision via web diffs.
  - Updated a revision via web diffs.
  - Edited a revision via web.
  - Edited nonstandard custom fields ("Blame Revision", "JIRA Issues").
  - Created a revision via CLI.
  - Updated a revision via CLI.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11114

Differential Revision: https://secure.phabricator.com/D17054

src/applications/differential/controller/DifferentialRevisionViewController.php

@@ -570,7 +570,7 @@ final class DifferentialRevisionViewController extends DifferentialController {
     $curtain->addAction(
       id(new PhabricatorActionView())
         ->setIcon('fa-pencil')
-        ->setHref("/differential/revision/edit/{$revision_id}/")
+        ->setHref("/differential/revision/editpro/{$revision_id}/")
         ->setName(pht('Edit Revision'))
         ->setDisabled(!$can_edit)
         ->setWorkflow(!$can_edit));