Add example allOf with single ref (#10948)

* Add example allOf with single ref

* fix dart-dio-next handling of that case

* Refactor without vendor extension

* Regenerate newer samples

samples/server/petstore/php-laravel/lib/app/Models/User.php

@@ -33,4 +33,7 @@ class User {
     /** @var int $userStatus User Status*/
     private $userStatus;
 
+    /** @var UserType $userType */
+    private $userType;
+
 }

samples/server/petstore/php-laravel/lib/app/Models/UserType.php

@@ -0,0 +1,12 @@
+<?php
+/**
+ * UserType
+ */
+namespace app\Models;
+
+/**
+ * UserType
+ */
+class UserType {
+
+}