Provide a smoother "update diff" web workflow

Summary:
Fixes T1102. If you don't use `arc`, the web workflow requires some extra needless steps when updating diffs.

Provide a more streamlined "Update Diff" workflow.

Test Plan: {F347750}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1102

Differential Revision: https://secure.phabricator.com/D12131

src/applications/differential/controller/DifferentialRevisionViewController.php

@@ -525,6 +525,13 @@ final class DifferentialRevisionViewController extends DifferentialController {
       ->setDisabled(!$can_edit)
       ->setWorkflow(!$can_edit);
 
+    $actions[] = id(new PhabricatorActionView())
+      ->setIcon('fa-upload')
+      ->setHref("/differential/revision/update/{$revision_id}/")
+      ->setName(pht('Update Diff'))
+      ->setDisabled(!$can_edit)
+      ->setWorkflow(!$can_edit);
+
     $this->requireResource('phabricator-object-selector-css');
     $this->requireResource('javelin-behavior-phabricator-object-selector');