build(docs-infra): update @angular/cli to 10.0.0-next.3 (#36145)

Update the Angular CLI and Angular framework packages to latest `@next`
versions. Also, update the app to look more closely to how a newly
generated app with the latest CLI would look like.

PR Close #36145

aio/src/polyfills.ts

@@ -35,7 +35,7 @@
  * will put import in the top of bundle, so user need to create a separate file
  * in this directory (for example: zone-flags.ts), and put the following flags
  * into that file, and then add the following code before importing zone.js.
- * import './zone-flags.ts';
+ * import './zone-flags';
  *
  * The flags allowed in zone-flags.ts are listed here.
  *