Secondary split screen app will be next to the navigation bar (1/2)

Refactored docked position code into PhoneWindowManager to determine
which side the docked app should go based on the position of the nav bar
in landscape (as portrait will only have top). Fixed the split screen
entrance animation for quick step's overview.

Change-Id: I30f1be9d791c23f4cd197f17487609964f78fac0
Fixes: 73250406
Test: play around with splitscreen and minimized mode
Test: atest com.android.server.policy.PhoneWindowManagerTest