Add new ExpandableNotificationRowController.

This is a further step towards moving testable logic out of our views.
It includes a moderate amount of refactoring in
NotificationRowBinderImpl, using the controller to fill in values on
the view that the binder used to fill in. It actually addresses some
outstanding TODOs in the process.

Bug: 147245740
Test: atest SystemUITests
Change-Id: I1537977438e74f85bba3c13e224d96ef49bc6bd9