#3274419 Makes BaseFieldOverride inherit the internal property from the base field.

Closes #3274419

core/lib/Drupal/Core/Field/Entity/BaseFieldOverride.php

@@ -145,6 +145,13 @@ public function isComputed() {
     return $this->getBaseFieldDefinition()->isComputed();
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function isInternal() {
+    return $this->getBaseFieldDefinition()?->isInternal();
+  }
+
   /**
    * {@inheritdoc}
    */