Change app component declaration from arrow function to regular function

[iansu]

Small update to the default templates to keep them consistent with the React docs.

[amshtemp]

@iansu
function App(): React.FC { }
vs.
const App: React.FC = () => {}

aren't those different (return type vs function type)?

[iansu]

@amshtemp Yes they are different. We're probably going to change the TypeScript template back to an arrow function.

[petetnt]

LGTM