style(docs-infra): fix docs examples for tslint rule semicolon (#38143)

This commit updates the docs examples to be compatible with the
`semicolon` tslint rule.

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/testing/src/app/demo/demo.ts

@@ -51,7 +51,7 @@ export class MasterService {
 export class ReversePipe implements PipeTransform {
   transform(s: string) {
     let r = '';
-    for (let i = s.length; i; ) { r += s[--i]; };
+    for (let i = s.length; i; ) { r += s[--i]; }
     return r;
   }
 }

aio/content/examples/testing/src/app/hero/hero-list.component.spec.ts

@@ -139,5 +139,5 @@ class Page {
     // Get the component's injected router navigation spy
     const routerSpy = fixture.debugElement.injector.get(Router);
     this.navSpy = routerSpy.navigate as jasmine.Spy;
-  };
+  }
 }

aio/content/examples/testing/src/app/welcome/welcome.component.spec.ts

@@ -8,7 +8,7 @@ import { WelcomeComponent } from './welcome.component';
 class MockUserService {
   isLoggedIn = true;
   user = { name: 'Test User'};
-};
+}
 // #enddocregion mock-user-service
 
 describe('WelcomeComponent (class only)', () => {