Add state to service worker onNotificationReceived

[daniel-shuy]

Closes #64

Adds the following state to the service worker onNotificationReceived handler:

• instanceId
• publishId
• deviceId
• userId
• appInBackground
• hasDisplayableContent
• hasData

deviceId and userId are stored in IndexedDB. To avoid slowing down the notification, a Promise is used to perform the query asynchronously passed. The listener can then subscribe to the Promise to get the state, for example:

PusherPushNotifications.onNotificationReceived = async ({ pushEvent, payload, statePromise }) => {
  const { userId } = await statePromise;
  pushEvent.waitUntil(
    // custom notification handling logic
  );
};

Because these data are used by the event reporting, I've refactored PusherPushNotifications.reportEvent to reuse the same Promise, to avoid querying IndexedDB twice.