Fixed an issue where HUNs would be clipped on tablets

Because the NSSL can be inset, notifications can actually be
positioned outside of the container when HUNd. Our clipping
logic was assuming that our minimum position would be 0,
which is incorrect.
We now don't make such assumptions about minimum positions.

Fixes: 421318771
Test: atest SystemUITests
Flag: com.android.systemui.physical_notification_movement
Change-Id: I75dc0acde74d314d075ef67de7b40b14a9c0595a