Set root task focused if one of its children is focused

There are several "unorganized" non-root tasks that aren't available in
TaskOrganizer, e.g. Home, and when they are in focus no task in WM shell
is focused without this change.

Bug: 207687679
Test: dumpsys activity service SystemUIService WMShell
Test: atest WmTests:TaskTests#testPropagateFocusedStateToRootTask
Change-Id: I48dafb50d70eced55a883f50d84519f884233503