BUG: fix size of paint cursor on rotated acquisitions

Make sure to use a column of the rasToXY matrix that is in the plane
of the zoom.  This is needed because the slice node's field of view
in Z does not reflect the in-plane zoom.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22268 3bd1e089-480b-0410-8dfb-8563597acbee