De-dupe shortcuts with the same id as the main notification.

- Pass NotificationKeyData, which includes the shortcut id, instead of
  just the notification key from NotificationListener
- Remove the shortcut with the same shortcut id as the first
  notification, if it has one, in PopupPopulator#sortAndFilterShorcuts()
- Add some unit tests

Bug: 36571718
Change-Id: I308941b34c525b34686583476e3f82ccb8b7e2d8