fix: don’t use the global ng at all with closure enhanced optimizations

This is needed as:
- closure declares globals itself for minified names, which sometimes clobber our `ng` global
- we can't declare a closure extern as the namespace `ng` is already used within Google for typings for angularJS (via `goog.provide('ng....')`).

packages/goog.d.ts

@@ -0,0 +1,15 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+
+/**
+ * Typings for google closure.
+ */
+declare namespace goog {
+  export const DEBUG: boolean;
+}