Until now, the user code response it's buffered and serialized. This is
mismatching how Vercel works these days.
This PR enables streaming response in `vc dev` for Edge/Serverless.
As part of the implementation, the `node-bridge` which spawns a process
to consume the user code is not necessary anymore.
Some necessary files (like HTTP server helpers) have been moved to live
in node builder package instead.
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Co-authored-by: Ethan Arrowood <ethan.arrowood@vercel.com>
Co-authored-by: Sean Massa <EndangeredMassa@gmail.com>
