Initial PoC for saving and reloading model and layout.

Closes #3478299

src/Controller/ApiLayoutController.php

@@ -13,11 +13,17 @@ use Symfony\Component\HttpFoundation\JsonResponse;
 
 final class ApiLayoutController {
 
+  use NotTheGoodAutoSaveTrait;
+
   public function __invoke(FieldableEntityInterface $entity): JsonResponse {
     if ($entity->bundle() !== 'article') {
       throw new \LogicException('For now, this assumes the entity is an article!');
     }
 
+    if ($body = $this->getAutoSaveData($entity)) {
+      return new JsonResponse($body);
+    }
+
     $item = $entity->get('field_xb_demo')->first();
     assert($item instanceof ComponentTreeItem);
     $tree = $item->get('tree');