wasm-node: Add support for WebRTC

[tomaka]

See https://github.com/libp2p/specs/ for how to implement this.

Two things need to be done:

• Modify the networking code to support transport protocols that natively support substreams.
• Modify bindings-smoldot-light.js to support WebRTC.

[tomaka]

cc libp2p/specs#220

[tomaka]

As a small note, WebRTC is unfortunately not available from within JS workers (despite WebSockets being available, don't ask me), so we would have to do some messages exchanges between outside and inside the worker to make that work.

[tomaka]

Considering that we might need to add another encryption layer within the DTLS+SCTP stream, it makes sense to me to simply open one SCTP channel for everything and apply Noise+Yamux to it.

As such, I've crossed out the first point.

Modify the networking code to support transport protocols that natively support substreams.

Maybe it turns out that in the end we'll need to do it, but for now it's not necessary.

[tomaka]

WebRTC should solve a problem related to blacklisted IP addresses, which I won't go into details to avoid someone "exploiting" this (though it's not really an exploit, just a way to be annoying).

[melekes]

What's left from the transport perspective:

• submit a spec for WebRTC libp2p transport (was done by libp2p maintainers webrtc/: Add libp2p WebRTC browser-to-server spec libp2p/specs#412)
• finish feat: Add WebRTC transport libp2p/rust-libp2p#2622
• use the new transport in smoldot

[tomaka]

After #2352:

• Add support for a /webrtc (or similar) protocol in Multiaddr.
• Actually add support for WebRTC in the smoldot JS code (bindings-smoldot-js.ts).
• Finish the areas where Add support for "multi-stream connections" #2352 has left todos, mainly wasm-node/rust/src/platform. This will be more easily done once the JS supports WebRTC, so that we can actually test if things work.