1. `requireInteraction` already existed, but it doesn't do anything.
This patch makes it mean `scenario="reminder"` in the Windows
Toast notification schema: see
https://docs.microsoft.com/en-us/uwp/schemas/tiles/toastschema/element-toast.
2. `actions` is intended to eventually support the Chrome-only
extension to the Web Notifications API: see
https://developer.mozilla.org/en-US/docs/Web/API/Notification/actions.
3. We run into an `xpconnect` limit on the number of supported
parameters. Rather than bump the limit, which has global
consequence, I added a second `init*` method. The existing
abstraction is horrible, but I can't rework it within my
timelines. Should we choose to invest, we might migrate to WebIDL
so that we can sensibly use options objects.
Differential Revision: https://phabricator.services.mozilla.com/D150667