Route task merges through new editor

Summary:
Ref T2217. Ship "Merge in Duplicates" through the new editor. The only notable thing here is `setContinueOnMissingFields()`.

The problem this solves is that if you add a custom field and mark it as required, all existing tasks are "invalid" since they don't have a value, and trying to edit them will raise an error like "Some Custom Field is required!". This is fine for normal edits via the UI, since the user can just select/provide a value, but surgical edits to specific fields should just ignore these errors. Add the ability to ignore these errors and use it on all the field-speific editors.

Test Plan: Merged duplicates, including "invalid" duplicates with missing fields.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2217

Differential Revision: https://secure.phabricator.com/D7084

src/applications/maniphest/controller/ManiphestSubpriorityController.php

@@ -44,7 +44,8 @@ final class ManiphestSubpriorityController extends ManiphestController {
 
       $editor = id(new ManiphestTransactionEditorPro())
         ->setActor($user)
-        ->setContinueOnNoEffect($request->isContinueRequest())
+        ->setContinueOnMissingFields(true)
+        ->setContinueOnNoEffect(true)
         ->setContentSourceFromRequest($request);
 
       $editor->applyTransactions($task, $xactions);