Temporary patch www fork with prefixed APIs (#17103)

I'm doing this here instead of in the downstream repo so that if the
sync diff gets reverted, it doesn't revert this, too.

Once the sync has landed, and the callers are updated in www, I will
remove this.

packages/react-dom/src/client/ReactDOMFB.js

@@ -39,4 +39,12 @@ Object.assign(
   },
 );
 
+// TODO: These are temporary until we update the callers downstream.
+ReactDOM.unstable_createRoot = ReactDOM.createRoot;
+ReactDOM.unstable_createSyncRoot = ReactDOM.createSyncRoot;
+ReactDOM.unstable_interactiveUpdates = (fn, a, b, c) => {
+  ReactDOM.unstable_flushDiscreteUpdates();
+  return ReactDOM.unstable_discreteUpdates(fn, a, b, c);
+};
+
 export default ReactDOM;