QmlDesigner: Change default position of new cameras

Since the orientation has changed to right handed, z-value needs to be
flipped to make default position of cameras sensible.

Change-Id: Iff4bee5266fe81cdb519e3bf68e6f363bc7fd4ef
Fixes: QDS-1815
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>