Split screen via Task menu when grid_only_overview is enabled

- Also change to choose bottom right task for split when grid_only_overview is eanbled, as ordering of tasks changes with grid_only_overview

Fix: 309041108
Fix: 309044300
Test: com.android.wm.shell.flicker.service.splitscreen.platinum.EnterSplitScreenFromOverviewGesturalNavLandscape#enterSplitScreenFromOverview
Test: com.android.wm.shell.flicker.service.splitscreen.platinum.SwitchBetweenSplitPairsGesturalNavLandscape#switchBetweenSplitPairs
Change-Id: I6906ecb4851097aefc027d5fd689e8c2098404dc