enable networking for emscripten

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In case it helps improving the WASM port, I was able to perform a simple socket connection following these steps:

1. add these headers to blink.c; reference

#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#include <emscripten/websocket.h>
#include <emscripten/threading.h>
#include <emscripten/posix_socket.h>

static EMSCRIPTEN_WEBSOCKET_T bridgeSocket = 0;
#endif

2. make sure the WebSocket is ready when calling a method:

int main(int argc, char *argv[]) {
#ifdef __EMSCRIPTEN__
  if (!bridgeSocket) {
    bridgeSocket = emscripten_init_websocket_to_posix_socket_bridge("ws://localhost:8080");
    // Synchronously wait until connection has been established.
    uint16_t readyState = 0;
    do {
      emscripten_websocket_get_ready_state(bridgeSocket, &readyState);
      emscripten_thread_sleep(100);
    } while (readyState == 0);
  }
#endif
....

3. Link with flags -lwebsocket.js -sPROXY_POSIX_SOCKETS -sUSE_PTHREADS -sPROXY_TO_PTHREAD reference
4. Have a local server running; https://github.com/emscripten-core/emscripten/tree/main/tools/websocket_to_posix_proxy

./websocket_to_posix_proxy 8080

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