Turbopack: NFT followups (#72517)
Closes PACK-3421
Address PR feedback from https://github.com/vercel/next.js/pull/72305
When working on this, I uncovered another bug which will be handled in a
different PR.
Changes:
- Don't rely on `DiskFileSystem` but only via file paths and
`is_inside()`
- Put the `RebasedAsset` for externals on the `[project]/` fs (this way,
they aren't emitted either), i.e. don't perform any rebasing at all and
just reference the files where they are
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Co-authored-by: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>