Fix switching a background task into split screen unexpectedly

If a task in split starts a new task or an adjacent task, it will
put the current splitting task behine it in the split. But when
users switch to the backgrond task, we would like to launch it in
fullscreen since it's shoiwng as a fullscreen tile in overview.

To fix this, the patch evicts any non-visible tasks in split when
detecting it's going to recent. So background tasks won't be launched
into split screen from overview anymore.

Fix: 232497373
Test: manual
Test: pass existing tests
Change-Id: I577aeeabda76fab88cd734af32ea8a69083ad3d3