docs: add temporary flag to enable lazy loading

Context: angular/angular-cli#13524

Author: brandonroberts

aio/tools/examples/shared/boilerplate/common/src/tsconfig.app.json

@@ -9,6 +9,7 @@
     "**/*.spec.ts"
   ],
   "angularCompilerOptions": {
-    "enableIvy": "ngtsc"
+    "enableIvy": "ngtsc",
+    "allowEmptyCodegenFiles": true
   }
 }