fix(wasm): directly generate chunk exports

[pi0]

🔗 Linked issue

#1952

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

When annotating wasm (virtual) chunk dependencies with external: true, roll-up sometimes reverts them to the original external package as external in the bundle.

This PR uses a virtual module (non-externalized) + post-build transform to convert it to relative import to avoid rollup interfering.

Note: when option is enabled for iife/umd targets (cloudflare preset) the experimental module is still unsupported now with more explicit check.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.