Eliminates NotificationEntryManager.getNotificationLongClicker().

This method always returned NotificationGutsManager::openGuts, and only
existed so that CarSystemUI could override it to disable long presses.
In this change we accomplish this by making
NotificationStackScrollLayout injectable and providing a named flag for
whether to enable long presses or not as a dependency.  This means that
NotificationEntryManager is no longer involved in handling long presses,
and CarNotificationEntryManager no longer needs to exist.

Test: atest SystemUITests, manual
Change-Id: Iae78601fea498a37ed47ef9a114e50de1652b6a8