Short shelf on lockscreen that animates width with transition to shade

NotificationIconContainer provides the shortest shelf width based on
3 icons + 1 overflow dot.

Propagate fraction-to-shade from LockscreenShadeTransitionController
=> NSSLC => NSSL => NotificationShelf, which uses it to calculates shelf width

NSSL requests children update,
then NotificationShelf propagates shelf width
=> NotificationBackgroundView for corner roundness positioning
=> NotificationIconContainer to limit icons to new width

NotificationShelf ensures that only the visible part of the shelf is tappable.

Bug: 213480466
Test: NotificationShelfTest
Test: swipe down on lockscreen notifications, let go
	=> short shelf expands, retracts width
Test: swipe down on lockscreen notifications to go to unlocked shade
	=> short shelf expands to full width
Test: expand notification on lockscreen
	=> short shelf expands to full width as shade opens
Test: tap hidden/visible part of shelf
	=> only visible part of shelf launches full shade
Test: the above in LTR/RTL

Change-Id: I1d3f2a9077e6058d4459bb11602601c035b8043a