Wrap short shelf width to icon count when less than lockscreen max

Move width updates into #updateAppearance.

Use numViewsInShelf for smooth width transitions.

Bug: 213480466
Test: add notif, shelf expands
Test: swipe away notif, shelf shrinks
Test: tap hidden/visible part of shelf
  => only visible part of shelf launches full shade
Test: the above in LTR/RTL

Change-Id: Icf5bfa6f901267446bd2dd16b39a6290538541b6