mark factory as experimental

Author: jrushlow

src/Generator.php

@@ -160,6 +160,9 @@ public function createClassNameDetails(string $name, string $namespacePrefix, st
         return new ClassNameDetails($className, $fullNamespacePrefix, $suffix);
     }
 
+    /**
+     * @experimental The method signature may change, moved, or be removed.
+     */
     public function createClassHelper(string $fullyQualifiedClassName): TemplateClassHelper
     {
         return new TemplateClassHelper($fullyQualifiedClassName, $this->phpCompatUtil->canUseTypedProperties());