Summary:
paint together the cursor image and the extra dnd image if available
on X11 with QDrag::setHotspot is possible to control their relative
position, which doesn't seem to have a wayland protocol correspondence
so their relative position are controlled just by the hotspot of the cursor itself

Test Plan:
folder graphics from dolphin is painted correctly
{F8086937}

Reviewers: #plasma, #kwin, davidedmundson

Reviewed By: #plasma, #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D27174