add a CDN entry point, so we can collect its usage

Author: Feiyang1

packages-exp/firebase-exp/app/index.cdn.ts

@@ -0,0 +1,5 @@
+import { registerVersion } from '@firebase/app-exp';
+import { name, version } from '../package.json';
+
+registerVersion(name, version, 'cdn');
+export * from '@firebase/app-exp';

packages-exp/firebase-exp/app/index.ts

@@ -14,5 +14,8 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+import { registerVersion } from '@firebase/app-exp';
+import { name, version } from '../package.json';
 
+registerVersion(name, version, 'app');
 export * from '@firebase/app-exp';

packages-exp/firebase-exp/rollup.config.js

@@ -112,7 +112,7 @@ const appBuilds = [
    * App UMD Builds
    */
   {
-    input: 'app/index.ts',
+    input: 'app/index.cdn.ts',
     output: {
       file: 'firebase-app.js',
       sourcemap: true,