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/test.ts

@@ -118,6 +118,17 @@ describe('Angular Language Service', () => {
       offset: 28,
     });
     expect(resp2).toMatchGolden('quickinfo.json');
+
+    client.sendRequest('open', {
+      file: `${PWD}/project/app/widget.component.html`,
+    });
+
+    const resp3 = await client.sendRequest('quickinfo', {
+      file: `${PWD}/project/app/widget.component.html`,
+      line: 1,
+      offset: 19,
+    });
+    expect(resp3).toMatchGolden('quickinfo_externalTemplate.json');
   });
 
   it('should perform definition', async () => {