Moves fullscreen intent logic to NotificationActivityStarter.

This change generalizes the AlertTransferListener interface as described
in its javadoc in order to make it a general-purpose listener interface
for changes managed by NotificationEntryManager, then uses this
mechanism to move handling of fullscreen intents on incoming
notifications from NotificationEntryManager to
StatusBarNotificationActivityStarter.

Test: atest NotificationEntryManagerTest
Change-Id: Ie8cb510466b2750fa74ef093dcad0726cf17210d