test(language-service): Add external template (#30128)

This is in preparation for more rigorous testing of external templates, since it'll work differently under the new tsserver plugin model.

PR Close #30128

integration/language_service_plugin/project/app/app.component.ts

@@ -2,6 +2,6 @@ import { Component } from '@angular/core';
 
 @Component({
   selector: 'my-app',
-  template: `<h1>Hello {{name}}</h1>`,
+  template: `<h1>Hello {{name}}</h1><my-widget></my-widget>`,
 })
 export class AppComponent  { name = 'Angular'; }