WMShell signals when a task's visibility changes

If a freeform task's visibility changes (and it's not a move between
displays), then WMShell signals it so launcher can listen and show the
information to the user.

Test: atest ShellTaskOrganizerTests
Test: atest RecentTasksControllerTest
Flag: com.android.window.flags.enable_desktop_windowing_taskbar_running_apps
Bug: 333872717
Change-Id: I229de5c1f297960e99319ccc0f7523219770cd3e
4 files changed