Restrict maximum task title length to 255 characters

Summary:
A task title is supposed to summarize a task. For long novels, there is the task description.

Closes T15898

Test Plan: Go to http://phorge.localhost/maniphest/task/edit/form/default/ and enter a task title with multi-byte characters above the threshold, press "Enter".

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15898

Differential Revision: https://we.phorge.it/D25759

src/applications/maniphest/xaction/ManiphestTaskTitleTransaction.php

@@ -4,6 +4,7 @@ final class ManiphestTaskTitleTransaction
   extends ManiphestTaskTransactionType {
 
   const TRANSACTIONTYPE = 'title';
+  private $maximumTaskTitleLength = 255;
 
   public function generateOldValue($object) {
     return $object->getTitle();
@@ -78,6 +79,13 @@ final class ManiphestTaskTitleTransaction
           $xaction);
         continue;
       }
+      if (mb_strlen($new) > $this->maximumTaskTitleLength) {
+        $errors[] = $this->newInvalidError(
+          pht('Task title cannot exceed %d characters.',
+            $this->maximumTaskTitleLength),
+          $xaction);
+        continue;
+      }
     }
 
     if (!$errors) {