[Feature request] Pass data to Notification and retreive it on activate

[manijak]

We need a way to pass custom data payload (like UserId) to a notification when creating one, and be able to retrieve it in the NotificationCompleted event.

Example: If an app shows 5 notifications, like chat messages from 5 different users. We need to know who each notification belongs to when tapping the notification itself.

The NativeNotificationCompletedEventArgs does include a property called UserData, but it does not seem accessible via the API. It is only populated when the user types a reply in the notification itself.