Make the paste "Create" transaction take a file PHID instead of content

Summary:
Ref T4814. Although this approach made sense at one point, we have more file infrastructure now and T4814 will be easier if we just pass a PHID in.

Also swap Conduit over to use the Editor.

Test Plan:
  - Created a paste.
  - Created a paste via Conduit.
  - Verified that files had correct permissions and appropriate object links in Files.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4814

Differential Revision: https://secure.phabricator.com/D8969

src/applications/paste/controller/PhabricatorPasteEditController.php

@@ -95,12 +95,16 @@ final class PhabricatorPasteEditController extends PhabricatorPasteController {
 
       if (!$errors) {
         if ($is_create) {
+          $file = PhabricatorPasteEditor::initializeFileForPaste(
+            $user,
+            $v_title,
+            $v_text);
+
           $xactions[] = id(new PhabricatorPasteTransaction())
             ->setTransactionType(PhabricatorPasteTransaction::TYPE_CREATE)
-            ->setNewValue(array(
-              'title' => $v_title,
-              'text' => $v_text));
+            ->setNewValue($file->getPHID());
         }
+
         $xactions[] = id(new PhabricatorPasteTransaction())
           ->setTransactionType(PhabricatorPasteTransaction::TYPE_TITLE)
           ->setNewValue($v_title);