Feed Differential retitled: do not repeat the title twice

Summary:
This is a cosmetic modification for a specific Feed.

https://we.phorge.it/T15183

If you retitle a Diff (and you do nothing else), its Feed
is somehow too much verbose:

    ... retitled NEW_TITLE from OLD_TITLE to NEW_TITLE

In this specific case, the Feed now becomes shorter so that
the NEW_TITLE is not repeated twice:

    ... retitled NEW_TITLE from OLD_TITLE

Note that, if the title changes again, the Feed naturally comes
back as before so to mention the change and obviously without
any repetition. Example:

    ... retitled CURRENT_TITLE from OLD_TITLE to NEW_TITLE

Closes T15183

Test Plan:
- take a Diff named "OLD_TITLE" and retitle to "NEW_TITLE"
- visit the homepage and see "retitled NEW_TITLE from OLD_TITLE"
  (this means the new behavior works)
- retitle the Diff from "NEW_TITLE" to "CURRENT_TITLE"
- visit the homepage again and see "retitled CURRENT_TITLE from OLD_TITLE to NEW_TITLE"
  (this means the old behavior still works)

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: avivey, speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15183

Differential Revision: https://we.phorge.it/D25094

src/applications/differential/xaction/DifferentialRevisionTitleTransaction.php

@@ -23,6 +23,17 @@ final class DifferentialRevisionTitleTransaction
   }
 
   public function getTitleForFeed() {
+    $obj = $this->getObject();
+
+    // To avoid verbose messages we mention the current title just once
+    if ($obj && $obj->getTitle() === $this->getNewValue()) {
+      return pht(
+        '%s retitled %s from %s',
+        $this->renderAuthor(),
+        $this->renderObject(),
+        $this->renderOldValue());
+    }
+
     return pht(
       '%s retitled %s from %s to %s.',
       $this->renderAuthor(),