After reloading transactions for the recipient while building transaction mail, put them in the input order

Summary:
Ref T13303. In D20525 I fixed an issue where transaction rendering could use cached values with the wrong viewer by reloading transactions.

However, reloading transactions may also reorder them as a side effect, since `withPHIDs(...)` does not imply an order. This can make transaction rendering order in mail wrong/inconsistent.

Instead, reorder the transactions before continuing so mail transaction order is consistent.

Test Plan: Applied a group of transactions to a task, saw a more consistent rendering order in mail after the change.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13303

Differential Revision: https://secure.phabricator.com/D20563

src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php

@@ -3084,6 +3084,11 @@ abstract class PhabricatorApplicationTransactionEditor
             ->withObjectPHIDs(array($object->getPHID()))
             ->withPHIDs($xaction_phids)
             ->execute();
+
+          // Sort the mail transactions in the input order.
+          $mail_xactions = mpull($mail_xactions, null, 'getPHID');
+          $mail_xactions = array_select_keys($mail_xactions, $xaction_phids);
+          $mail_xactions = array_values($mail_xactions);
         } else {
           $mail_xactions = array();
         }