LibJS: Stub out Atomics.notify

We don't have the facilities to implement this method fully (namely, a
fully realized SharedArrayBuffer). But we can implement enough to
validate the values passed in by the user.

Userland/Libraries/LibJS/Runtime/AtomicsObject.h

@@ -32,6 +32,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(sub);
     JS_DECLARE_NATIVE_FUNCTION(wait);
     JS_DECLARE_NATIVE_FUNCTION(wait_async);
+    JS_DECLARE_NATIVE_FUNCTION(notify);
     JS_DECLARE_NATIVE_FUNCTION(xor_);
 };