This PR adds support for [Middleware as per RFC ](https://github.com/vercel/next.js/discussions/29750).
## 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
Removes the extra webpack handling that was previously done, this ensures the file which is already minified and compiled does not get passed through minification again.
Largely based on #21418Closes#21418
The polyfill loading already has tests so no other changes are necessary.
## 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
We generate the HTML for a document in two steps: First, we generate the body (i.e. everything under `<div id="__next">`). Then we generate the rest of the document and embed the body in it.
This doesn't work when the body is a stream, because React can't render the body for us unless we buffer it, and buffering it means not streaming. This PR takes the existing approach for AMP and uses it for all scenarios: instead of rendering HTML, we just render a placeholder that we can replace with HTML later. This will be used in a follow-up PR to let us know where to concatenate the body stream.
I also used the opportunity to split out `HtmlContext` from `DocumentProps`, as these will not be the same thing with functional document components.