feat: Use concurrent React when available (#937)

BREAKING CHANGE: If you have React 18 installed, we'll use the new [`createRoot` API](https://github.com/reactwg/react-18/discussions/5) by default which comes with a set of [changes while also enabling support for concurrent features](https://github.com/reactwg/react-18/discussions/4).
To can opt-out of this change by using `render(ui, { legacyRoot: true } )`. But be aware that the legacy root API is deprecated in React 18 and its usage will trigger console warnings.