Turbopack: Improve unable to resolve next error (#91394)
## What
Improves the error message shown when Turbopack cannot resolve the
`next` package. The issue now includes the filesystem root used for
resolution, making it easier to diagnose misconfigured `turbopack.root`
settings.
## Why
When `next` can't be resolved, the previous error message showed the
context directory but not the root used for resolution. This made it
difficult to determine whether the resolution root was incorrect,
especially in monorepo setups.
## Changes
- Added `root` field to `MissingNextFolderIssue` to track the filesystem
root used for resolution
- Display the filesystem root path in the error message
- Updated the fix suggestion to reference "project directory" instead of
"this directory" for clarity
