Remove badges when launcher loses notification access

- NotificationListener.getInstance() has been changed to
  getInstanceIfConnected() (same behavior as before).
- When starting launcher, we send a full refresh of badges
  regardless of whether the NotificationListner is connected.
  If it is not connected, we pass an empty list for the
  active notifications, so that all pre-existing badges are
  removed.

Bug: 35221052
Change-Id: If920317f10814c010e02b5a30ce86a58ac7bc61c