Networking and connectivity support in WebAssembly

Collection of networking and connectivity related tickets in WebAssembly (wasm)

Works Today:
-QNetworkAccessManager http(s) requests to the web page origin server, or to a server which supports CORS.
-QWebSocket connections to any host.
Issue
-TCP and UDP sockets are not well supporte
-Blocking sockets on the main thread not supported
-Sockets on a secondary thread is not supported
Solution: 
-Tunnel TCP and UDP sockets over WebSockify, using functionality provided by Emscripten.
-Event dispatcher socket notifier support for async (nonblocking) sockets on the main thread
-Use asyncify for blocking sockets on the main thread.
-Local socket proxy towards the HTTP server
https://emscripten.org/docs/porting/networking.html#:~:text=Emscripten%20provides%20a%20native%20POSIX%20Sockets%20proxy%20server,POSIX%20Sockets%20API%20access%20from%20a%20web%20browser.

Blocking sockets are handled in QTBUG-76739