Blitz: Enable React Fast Refresh

[merelinguist]

What do you want and why?

We should enable Fast Refresh for apps by default.

Implementation

1. Add the fastRefresh flag inside the withBlitz config wrapper

  experimental: {
    reactRefresh: true
  }

1. Upgrade Next.js to latest canary (>= 9.3.7-canary.5)

See here for an explanation: https://github.com/zeit/next.js/pull/12008

[Timer]

This feature is not ready to be enabled by default. Please do not enable it for all users until (at a minimum) https://github.com/zeit/next.js/pull/12222 has been landed.

[merelinguist]

@timer Oh, okay! I saw a tweet from Dan asking people to try it out so I assumed it was at least alpha-ready. Thanks so much for the heads up 👍

[Timer]

For posterity: https://twitter.com/dan_abramov/status/1255233660317503490

[flybayer]

Thanks @timer!

Reopening this because we still want to do it at some point

[Timer]

Good to enable now if the underlying Next version is ^9.3.7-canary.5 or newer.

[flybayer]

Awesome, thank you @Timer!!

[0ww]

Thank you very much, @dwightwatson !