dillon1000/react

act: Bypass microtask for "default sync" updates (#21740)

When wrapping an update in act, instead of scheduling a microtask,
we can add the task to our internal queue.

The benefit is that the user doesn't have to await the act call. We can
flush the work synchronously. This doesn't account for microtasks that
are scheduled in userspace, of course, but it at least covers
React's usage.