docs(upgrade): use a class for upgraded service (#18487)

This makes the resulting use in Angular more ideomatic, since we can just
use the class type as the injection indicator.

PR Close #18487

packages/upgrade/src/static/upgrade_module.ts

@@ -127,7 +127,7 @@ import {NgAdapterInjector} from './util';
  *
  * Let's say you have an AngularJS service:
  *
- * {@example upgrade/static/ts/full/module.ts region="ng1-title-case-service"}
+ * {@example upgrade/static/ts/full/module.ts region="ng1-text-formatter-service"}
  *
  * Then you should define an Angular provider to be included in your `NgModule` `providers`
  * property.