Check for desk root in getFocusedNonDesktopTasks.

Adds a check for desk root in getFocusedNonDesktopTasks. The current
check for focused non-desktop tasks checks if the task is not in task
repository and is neither home nor wallpaper. Desk roots fit all these
criteria and can be focusable.

Bug: 423483536
Flag: com.android.window.flags.exclude_desk_roots_from_desktop_tasks
Test: Manual, tab tear does not no-op due to focused desk
Change-Id: I586f0c8d55af6395636e5d8849ad5c5c9afab939