Fix unexpected full hmr reload when editing _app (#54690)
### What
When you only have `pages/` folder and custom `_app.js`, editing the
`_app.js` file when unexpectedly lead to full page reload. This is
because the `pages/_app` chunk is included into `pages/_document` chunk
as they all pass through the `next-route-loader` which forms the router
module and other userland modules including `/_app` and `/_document`.
That leads to a change: whenever you modify `_app.js`, chunk hash of
`/_document` will always be updated as it's built as a new chunk.
Found this difference by looking at the document chunk with nextjs in
early 13.4.x releases.
### How
We'll check at the entries creation point to filter out `/_app` and
`/_document` so that we won't have them both bundled for `_document`
chunk. Then when we won't trigger the hmr path to reload the page since
_document chunk hash is updated.
Closes NEXT-1568
Fixes #53614
