Declare class property for the DateTime data processer

Closes #3476099

src/Plugin/ExternalEntities/DataProcessor/DateTime.php

@@ -30,6 +30,13 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
  */
 class DateTime extends DataProcessorBase {
 
+  /**
+   * The typed data manager.
+   *
+   * @var \Drupal\Core\TypedData\TypedDataManagerInterface
+   */
+  protected TypedDataManagerInterface $typedDataManager;
+
   /**
    * Constructs a DateTime processor object.
    *