Fix bug with portrait-fold devices animating app pairs launch wrongly

This CL makes it so that isLeftRightSplit is correctly called instead of isLandscape when animating an app pair launch.

Fixes: 318756992
Test: Manual
Flag: ACONFIG com.android.wm.shell.enable_app_pairs TEAMFOOD
Change-Id: Id766a3f9bd315abc277e36a118fd233156cf3898