Turbopack: Refactor resolver to accept bool instead of severity (#71254)
I pulled out the core change from
https://github.com/vercel/next.js/pull/71155
- Refactor resolve functions to accept a `is_optional` boolean instead
of an explicit severity
- Add `ResolveOptions::loose_errors` to only emit warnings instead of
errors
Not sure if `loose_errors` is the best name. `warn_instead_of_errors`,
`emit_warnings_only` ?