* remove the experimental web vital hook api
* remove the exported flush effects api and only error on development, keep only usage to styled-jsx
for web vital hook API: The usage is not widly adopted since the existing exported vital api could do the same work. In the future we'll deprecate the `_app.server` in favor of `_app` in server component pages. so that this api won't be required.
for flush effects api: other css-in-js libs are not using the same approach like styled-jsx which holding a style registry and could flush it during streaming. emotion-js and styled-components are still relying on `Document.getInitialProps` atm and we have supported it in latest canary
Move undocumented `next/rsc` and `next/vitals` to `next/streaming`. In the future `next/streaming` can contain streaming SSR related (including react server components) APIs together.
## Bug
fixes#32631
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [x] Errors have helpful link attached, see `contributing.md`
