feat: mark angular packages as side-effect free (#22785)

This flag is picked up by webpack v4 and used for more agressive optimizations.

Our code is already side-effect free, because that's what we needed for build-optimizer to work.

PR Close #22785

packages/platform-server/package.json

@@ -27,5 +27,6 @@
   },
   "ng-update": {
     "packageGroup": "NG_UPDATE_PACKAGE_GROUP"
-  }
+  },
+  "sideEffects": false
 }