bridge: emit message event inside a setImmediate

Emit the bridge's message event inside a setImmediate, so listener
code is called outside the napi scope created when the bridge
receives a call from the react-native application code.
This allows for promises started on the listeners to be resolved and
causes errors to be recognized by the javascript engine instead of
silently failing.

install/resources/nodejs-modules/builtin_modules/rn-bridge/index.js

@@ -10,7 +10,9 @@ MyEmitter.prototype.send=function(msg) {
 const channel = new MyEmitter();
 
 var myListener = mybridgeaddon.registerListener( function(msg) {
-  channel.emit('message', msg);
+  setImmediate( () => {
+    channel.emit('message', msg);
+  });
 });
 
 exports.channel = channel;