Support Fast Refresh

## Describe the feature

We've landed [Fast Refresh](https://mobile.twitter.com/reactnative/status/1144629612921720833) on React Native master. You can try it if you build all Metro packages from master and replace them in `node_modules` of RNTester.

## Motivation

It would be nice if Haul could replace `react-hot-loader` or other techniques with Fast Refresh because:

- Fast Refresh doesn't create semantic differences in behavior (so it's safe to always leave on, unlike solutions based on `react-hot-loader` and similar tools)
- Fast Refresh fully supports function components and Hooks, including cases where you add or remove Hooks
- Fast Refresh gracefully recovers from errors

It likely also fixes hot reloading problems with navigation libraries because it's fully integrated with React. (Although I don't have a test case to verify that.)

It would also unify the behavior with mainline React Native.

## But How?

I'd be happy to chat with someone to give an overview of how the new system works. For a 100% match in behavior we might need some new hooks from webpack, but you should be able to get reasonably close today too.