Upgrade to react/react-dom ^16.9.0 once released

Right now we use a prerelease version of `react` and `react-dom`

- [ ] Replace all fixed `react`/`react-dom` dependencies with version range `^16.9.0`
- [ ] Remove `"resolutions"` entries in root package.json

See https://github.com/facebook/react/pull/16254 