Merge debugger-proxy of RN packager into debugger client

We could merge [the debugger proxy](https://github.com/facebook/react-native/blob/34487c059192129db07608af4eb27cfad22b2d06/local-cli/server/util/webSocketProxy.js), this will reduce the cost of connection with react-native app:

* Open a WebSocket server (`/debugger-proxy`) with some port, instead of RN packager
* Need to figure out how easy to change debugger-proxy port in react-native app

Start by reading the linked React Native debugger proxy implementation in local-cli/server/util/webSocketProxy.js and tracing how the debugger client connects to the packager. Investigate how the React Native app selects the debugger-proxy port. Done means the proxy is hosted by the debugger client and the app can connect to its chosen port without the packager hosting it.

Scritto dal modello di indicizzazione a partire dal testo della issue.