LibWeb: Mark IDBFactory.open() with FIXME extended attribute in IDL

The stub implementation broke x.com and probably other sites as well,
but let's at least mark it FIXME so we get some debug logging about it.

Userland/Libraries/LibWeb/IndexedDB/IDBFactory.idl

@@ -1,8 +1,8 @@
 // https://w3c.github.io/IndexedDB/#idbfactory
 [Exposed=(Window,Worker)]
 interface IDBFactory {
-    // FIXME: [NewObject] IDBOpenDBRequest open(DOMString name,
-    //                                          optional [EnforceRange] unsigned long long version);
+    [FIXME, NewObject] IDBOpenDBRequest open(DOMString name,
+                                             optional [EnforceRange] unsigned long long version);
     [FIXME, NewObject] IDBOpenDBRequest deleteDatabase(DOMString name);
 
     [FIXME] Promise<sequence<IDBDatabaseInfo>> databases();