chore(ngUpgrade): Move into Angular2

This is moving ngUpgrade into the main repository per #4838.
The ngUpgrade is published from the main import consistent with
https://docs.google.com/document/d/1rbVTKTYLz6p2smQNYI8h4-QN-m2PS6F3iQIDmSzn0Ww/edit#heading=h.6cxvr9awtf5r
Closes #4931

modules/angular2/upgrade.ts

@@ -0,0 +1,6 @@
+/**
+ * @module
+ * @description
+ * Adapter allowing AngularJS v1 and Angular v2 to run side by side in the same application.
+ */
+export {UpgradeAdapter, UpgradeAdapterRef} from './src/upgrade/upgrade_adapter';