fix(language-service): Insert parentheses for method completion (#33860)

This commit leverages the `insertText` field in `ts.CompletionEntry` to
return a completion text for class methods that includes parentheses.

PR closes https://github.com/angular/vscode-ng-language-service/issues/15

PR Close #33860

packages/language-service/test/ts_plugin_spec.ts

@@ -128,6 +128,7 @@ describe('plugin', () => {
         kind: CompletionKind.PROPERTY as any,
         sortText: 'children',
         replacementSpan: {start: 182, length: 8},
+        insertText: 'children',
       },
     ]);
   });