Fixes few corner issues of multi-window windowing mode split-screen

- Updates the preferred top focused root task when a root task was
  added on top.

- Also updates the resumed activity (so as the focused app) while
  root task position changed.

- Do not resume the top activities of the tasks that are visible, but is
  behind other visible tasks (TASK_VISIBILITY_VISIBLE_BEHIND_TRANSLUCENT).

Bug: 177190100
Test: ActivityLifecycleLegacySplitScreenTests
Test: MultiWindowTests#testLaunchToSideAndBringToFront
Change-Id: Ied5041f3987a964931cdab508955759671336af4