Support keyboard long-press on notifications

ExpandableNotificationRow now handles long-clicks for keyboard support.
SwipeHelper calls performLongClick to trigger the listener on the row.
Now that the View listens to long clicks, SwipeHelper cancels
long-presses on the View when it see touch down events, so the event
doesn't get duped in the touch case.

Bug: 34840327
Test: manual
Change-Id: Ibeb93507781443d6b2dac209afd889b1d8d54aeb