Turbopack: support more dynamic request with import map (#84178)
Add support to resolve arbitrarily dynamic requests into a `'@/*": "./@"` import mapping, such as
```js
import(`@/styles/themes/theme-${themeName}/theme-${themeName}`)
```
Closes [#83785](https://github.com/vercel/next.js/issues/83785)
Closes PACK-5451
This was basically a regression from #82757