Turbopack NFT: trace manifests and externals (#72316)
- Change the Next manifest output assets to also track references to output assets there. That way, `page.js.nft.json` lists the referenced output assets of `page.js` and e.g. `page_client-reference-manifest.js` and all the chunks references in the manifest as well.
- For `ResolveResultItem::External`, continue resolving with a fresh `ModuleAssetContext` that doesn't have any of the build-time settings (because the Node environment when running the server won't have these settings either).
Closes PACK-3380
