refactor(docs-infra): fix docs examples for tslint rules related to object properties (#38143)

This commit updates the docs examples to be compatible with the
`no-string-literal`, `object-literal-key-quotes` and
`object-literal-shorthand` tslint rules.

This is in preparation of updating the docs examples `tslint.json` to
match the one generated for new Angular CLI apps in a future commit.

PR Close #38143

aio/content/examples/forms/src/app/hero-form/hero-form.component.ts

@@ -48,9 +48,9 @@ export class HeroFormComponent {
   // Reveal in html:
   //   Name via form.controls = {{showFormControls(heroForm)}}
   showFormControls(form: any) {
-    return form && form.controls['name'] &&
+    return form && form.controls.name &&
     // #docregion form-controls
-    form.controls['name'].value; // Dr. IQ
+    form.controls.name.value; // Dr. IQ
     // #enddocregion form-controls
   }