Preemptively adjust task info visibility when evicting tasks

- When a child of a split root is evicted, preemptively mark it as
  not visible to ensure that it isn't considered when reporting
  split pair tasks to the recent tasks controller.  This CL does not
  attempt to fix the underlaying problem that mChildrenTaskInfo does
  not track z-order while certain parts of the code already assume
  it does

Bug: 378030938
Bug: 378601156
Flag: EXEMPT bugfix
Test: atest WMShellUnitTests
Change-Id: Ib1bb621c6243f31fa7a4e25bff00714839154ff5