Show split options when overview actions hidden for grid

* We hide split option in task menu for focused task
if the user hasn't scrolled at all in overview
* We show option when user has scrolled because then
the split option from overview actions will be hidden
* Mostly uses the same logic as
RecentsView#updateActionsViewFocusedScroll()

Bug: 201380373
Test: Manual
Change-Id: Ia8769a67cfbb2e4414cd4d8e816e62245fc4bd2c