Minimal duplicate create hook implementation

Closes #3040556

core/lib/Drupal/Core/Entity/ContentEntityBase.php

@@ -1217,6 +1217,11 @@ public function createDuplicate() {
       $duplicate->loadedRevisionId = NULL;
     }
 
+    // Modules might need to add or change the data initially held by the new
+    // entity object, for instance to fill-in default values.
+    \Drupal::moduleHandler()->invokeAll($this->getEntityTypeId() . '_duplicate', [$duplicate, $this]);
+    \Drupal::moduleHandler()->invokeAll('entity_duplicate', [$duplicate, $this]);
+
     return $duplicate;
   }