Update desktop mode to identify minimized tasks

When a task is minimised, it becomes invisible but is still running.
WMShell now signals to the launcher when a task's visibility changes.
The task bar takes the visibility into account to know if a running task
is, in fact, minimised.

Test: atest NexusLauncherTests:DesktopTaskbarRunningAppsControllerTest
Flag: com.android.window.flags.enable_desktop_windowing_taskbar_running_apps
Bug: 333872717
Change-Id: Iaff6b1240d354bb3c4de8e4884948acf9bf40112