dillon1000/react

[Test] Update `flushSync` tests to use react-dom (#28490)

Updates the `flushSync` tests to use react-dom instead of ReactNoop.
flushSync is primarily a react-dom API and asserting the implementation
of ReactNoop is not really ideal especially since we are going to be
refactoring flushSync soon to not be implemented in the reconciler
internals.

ReactNoop still have a flushSync api and it can still be used in other
tests that are primarily about testing other functionlity and use
ReactNoop as the renderer.