This replaces the server-sent events HMR connection with a WebSocket connection to prevent hitting browser connection limits, allow sending events back from the browser, and overall better performance.
This approach sets up the the `upgrade` event listener on the server immediately when created via `next dev` and on the first request using `req.socket.server` when created via a custom server. In a follow-up PR we can push the files changed via the WebSocket as well.
x-ref: https://github.com/vercel/next.js/issues/10061
x-ref: https://github.com/vercel/next.js/issues/8064
x-ref: https://github.com/vercel/next.js/issues/4495
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes
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