The previous code gets the user's reading position *once*, when the
viewmodel is created, and uses that whenever it needs to be restored.
This is a problem. Suppose the user is a few days behind on their
notifications, and opens the app.
The reading position is restored, as expected. They scroll up to start
reading newer notifications.
Then they change their notification filters. This causes the
notifications list to change, and when it does their reading position
is set back to what it was when they first switched to the Notifications
tab.
Fix this by:
NotificationsFragment:
- Save the reading position whenever the user stops scrolling.
NotificationsViewModel:
- Use the saved reading position whenever the list of notifications
can change, not just when the view model is created.
57e79b3f00