JS apps support 1/n

Summary:
### Connecting Flipper with JS apps by using electron's BrowserWindow and IPC

1. UI: there is a menu item in Devices tab which opens JS Emulator Launcher Sheet. Here we can configure URL to open and initial size of the window.
2. BrowserWindow, preloaded js: there is SupportJSClientPreload.js which initialize communication between flipper and app via electron's ipc
3. On flipper's side there is src/utils/js-client/serverUtils.tsx which contains most of JS emulator related code
4. Extracting of FlipperClientConnection: since we don't use RScocket to communicate with JS app I extracted needed methods to FlipperClientConnection (located in Client) and partly implemented them in JSClientFlipperConnection (requestResponse is just send a message now, doesn't return actual result)

Reviewed By: jknoxville

Differential Revision: D18572882

fbshipit-source-id: 56d1ca1a60ed2e51329b917021a09382cbb1ceec

src/server.tsx

@@ -16,17 +16,19 @@ import {RSocketServer} from 'rsocket-core';
 import RSocketTCPServer from 'rsocket-tcp-server';
 import {Single} from 'rsocket-flowable';
 import Client from './Client';
+import {FlipperClientConnection} from './Client';
 import {UninitializedClient} from './UninitializedClient';
 import {reportPlatformFailures} from './utils/metrics';
 import EventEmitter from 'events';
 import invariant from 'invariant';
 import tls from 'tls';
 import net, {Socket} from 'net';
-import {RSocketClientSocket} from 'rsocket-core/RSocketClient';
 import {Responder, Payload, ReactiveSocket} from 'rsocket-types';
+import GK from './fb-stubs/GK';
+import {initJsEmulatorIPC} from './utils/js-client/serverUtils';
 
 type ClientInfo = {
-  connection: RSocketClientSocket<any, any> | null | undefined;
+  connection: FlipperClientConnection<any, any> | null | undefined;
   client: Client;
 };
 
@@ -84,6 +86,11 @@ class Server extends EventEmitter {
         return;
       });
     reportPlatformFailures(this.initialisePromise, 'initializeServer');
+
+    if (GK.get('flipper_js_client_emulator')) {
+      initJsEmulatorIPC(this.store, this.logger, this, this.connections);
+    }
+
     return this.initialisePromise;
   }
 
@@ -304,7 +311,7 @@ class Server extends EventEmitter {
   }
 
   async addConnection(
-    conn: RSocketClientSocket<any, any>,
+    conn: FlipperClientConnection<any, any>,
     query: ClientQuery,
     csrQuery: ClientCsrQuery,
   ): Promise<Client> {