Implement Direct Sockets API

[meponderR]

The Direct Sockets API is currently in trial in chrome://flags. If this were to be implemented it would allow network sockets to work within Emscripten in a web browser without the need of a proxy.

[sbc100]

That does look promising. Looks like it should be fairly simple to hook up to our posix socket layer if anyone wants to have a go.

[guest271314]

Here's my implementation of TCPSocket and UDPSocket using IPC via Web extension external_connecatable, written to WHATWG Streams https://github.com/guest271314/sockets/blob/main/sockets-web-extension/direct-socket.js.