chore: upgrade to create-react-app 5

[mrnerdhair]

Description

Good news: closes #589, closes #605, closes #549

Bad news: Webpack 5 dropped support for node polyfills; note facebook/create-react-app#11756, which basically says "whatever, not our problem" about it. Now we have to provide our own. Webpack can detect all the modules that need to be included, but ops testing will be needed to discover if any errors are triggered by modules which are using any more Node globals.

Notice

Before submitting a pull request, please make sure you have answered the following:

• Have you followed the guidelines in our Contributing guide?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Do all new and existing tests pass? Does the linter pass?

Pull Request Type

• 🐛 Bug fix (Non-breaking Change: Fixes an issue)
• 🛠️ Chore (Non-breaking Change: Doc updates, pkg upgrades, typos, etc..)
• 💅 New Feature (Breaking/Non-breaking Change)

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Pages

Latest commit:	90b144d
Status:	✅  Deploy successful!
Preview URL:	https://6d571025.web-29e.pages.dev

View logs

[mrnerdhair]

Note the patch-package stuff can go once timarney/react-app-rewired#589 is merged, and it looks like that'll happen quite soon.

[mrnerdhair]

There are a few new linter rules; testing-library/no-unnecessary-act says to remove await act() wrappers from various tests, but there are three that hang if not wrapped. @toshiSat, any feedback on whether to remove all the wrappers that don't break the tests, or to disable the eslint rule each time?

[mrnerdhair]

timarney/react-app-rewired#589 was merged this morning, and I've updated and dropped the interim patch-package hack.