FE API: disable cart migrating functionality

- the current cart migration implementation does not work in the FE API so it is useless and dangerous to even try it (the session is started in the process which is unwanted in the API)

packages/framework/src/Model/Cart/CartMigrationFacade.php

@@ -88,6 +88,11 @@ public function mergeCurrentCartWithCart(Cart $cart): void
      */
     public function onKernelController(ControllerEvent $event): void
     {
+        $controller = $event->getController();
+        $frontendApiControllerName = 'Shopsys\FrontendApiBundle\Controller\FrontendApiController';
+        if (class_exists($frontendApiControllerName) && isset($controller[0]) && get_class($controller[0]) === $frontendApiControllerName) {
+            return;
+        }
         $session = $event->getRequest()->getSession();
 
         $previousCartIdentifier = $session->get(static::SESSION_PREVIOUS_CART_IDENTIFIER);