Explicitly set X and Y values when offsetting split tasks

* Race condition where DeviceProfile that gets set on
TaskViewSimulator initially has incorrect values
(dp.isLandscape is incorrect)
* The correct one eventually gets set, but in the meantime
we set the split offset assuming in incorrect value in
PagedOrientationHandler#setLeashSplitOffset()
* Once corrected, we weren't removing the old offset
that was set. Now we ensure only either an X or Y offset set.

Bug: 199376724
Test: Enter split, rotate device and quickswitch.
Both tasks should be visible throughout the gesture

Change-Id: I9fa44642ab440a0200c0b0eb9b37574e47b7100d