LibJS: Convert FinalizationRegistry::cleanup to ThrowCompletionOr

Author: https://github.com/davidot
Commit: f324d91106
Pull-request: https://github.com/SerenityOS/serenity/pull/12343
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibJS/Runtime/FinalizationRegistry.h

@@ -28,7 +28,7 @@ public:
 
     void add_finalization_record(Cell& target, Value held_value, Object* unregister_token);
     bool remove_by_token(Object& unregister_token);
-    void cleanup(FunctionObject* callback = nullptr);
+    ThrowCompletionOr<void> cleanup(FunctionObject* callback = nullptr);
 
     virtual void remove_dead_cells(Badge<Heap>) override;