At least on X11 this is a real hierarchy: slave devices come and go
as children of the master devices. The goal is to verify that this tree
and the output of `xinput list` are in sync. The model calls
[begin|end]InsertRows() and [begin|end]RemoveRows() as necessary to
attempt to keep the view updated.
Task-number: QTBUG-46412
Task-number: QTBUG-98720
Task-number: QTBUG-104878
Task-number: QTBUG-112141
Change-Id: I8a2252f041cd1de777eef225d0e7f0db5c90a706
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
