Update service worker when new version is detected

[Rich-Harris]

Describe the problem

With #3412, SvelteKit can detect when new versions of the app have been deployed. It would be useful if the service worker was updated when that happens, if one exists.

Describe the proposed solution

Inside the code that checks for updates, something like this:

const registration = await navigator.serviceWorker.getRegistration(base || '/');

if (registration) {
  registration.update();
}

Alternatives considered

No response

Importance

nice to have

Additional Information

No response