Fixed the shadows on the lockscreen for bypass

The shadows were clipped before which made them appear
very jarringly. They now appear smoother.
Also, the shelf wasn't actually hidden when it was fully
clipped leading to an ugly remainder on the lockscreen

Fixes: 138258095
Test: atest SystemUITests
Change-Id: I070c307119572aa41423d1370a55010b2f428be4