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.module.ts

@@ -2,10 +2,11 @@ import { NgModule }      from '@angular/core';
 import { BrowserModule } from '@angular/platform-browser';
 
 import { AppComponent }  from './app.component';
+import { WidgetComponent } from './widget.component';
 
 @NgModule({
   imports:      [ BrowserModule ],
-  declarations: [ AppComponent ],
+  declarations: [ AppComponent, WidgetComponent ],
   bootstrap:    [ AppComponent ]
 })
 export class AppModule { }