Handle the uncontrolled task in split-screen

Exit the split-screen in case users put the uncontrolled task into
split-screen. This CL do below change to support handling this task.
   1. If no controlling activity appeared, dismiss the split screen
      and show a toast to inform users.
   2. Reparent all tasks out of split root when dismissing instead of
      just reparent controlling tasks.
   3. Disable the split-item from launcher for tasks that are
      uncontrolled.

Bug: 230461945
Bug: 208646963
Bug: 238032411
Test: atest MultiWindowTests
      atest WMShellUnitTests
Change-Id: Iab59561e9d532b10dab8f5063047c4b68b73eb87