iOS bridges need to take into account bridge changes

New bridges (and the existing bridge) needs to take into account bridge changes.

Each bridge should have this at the end of their .js:

// unregister the old bridge
cordova.define.remove('cordova/exec');
// redefine bridge to our new bridge
cordova.define("cordova/exec", function(require, exports, module) {
    module.exports = iOSExec;
});

But, this would only re-define cordova.exec and the return value of `require('cordova/exec')`. However, if the bridge was not loaded first, existing local references in plugins to `require('cordova/exec')` will not be updated.

Therefore, each bridge itself must detect that it is not the current bridge, and forward commands to the new bridge. Thus:

var iOSExec = function() {
      if (iOSExec !== cordova.exec) {
          cordova.exec.apply(null, arguments);
          return;
      }

// ... rest of the implementation here...
}

Although I see this being a problem of the default bridge, not any external bridges.

There might be an edge case where a command is already in the commandQueue (default bridge) when the bridge is swapped, that needs to be handled.

I realize this seems hacky, but if there's a better way to handle this case I'm all ears.