ready promise doesn't work right when controlling registration is resurrected

I was debugging some intermittent failures in our tests when I noticed some strange behavior. Consider:

  // start with a service worker
  let reg = await navigator.serviceWorker.register(script);
  await waitForState(reg.installing, "activated");

  // get a controlled document to hold the worker alive
  let frame = await withIframe(controlledURL);

  // mark the registration as uninstalling, but it won't
  // fully uninstall because of the frame
  await reg.unregister();
  
  // get the ready promise while in the uninstalling state
  let readyPromise = navigator.serviceWorker.ready;

  // register the service worker again, resurrecting the currently
  // active worker
  await navigator.serviceWorker.register(script);

  // this will never resolve
  await readyPromise;

I also wrote up a glitch to test this:

https://sw-ready-resurrection.glitch.me/

It seems both firefox and chrome have this problem. I think we should resolve the ready promise if we resurrect an uninstalling registration with an active worker and matching scope.

Start by reproducing the sequence in the issue and the linked sw-ready-resurrection.glitch.me test: register and activate a service worker, keep a controlled frame alive, unregister, obtain navigator.serviceWorker.ready, then register again. Compare the observed behavior with the service worker registration and ready-promise specification; done means the pending promise resolves after an uninstalling registration is resurrected with an active worker.