xdg-shell: fix maximizing in multi-head setup
xdg-shell: fix maximizing in multi-head setup

Set the right position of maximized window. Up until now we ignored
output's "position" and were using only the working area
of output which is in output-relative coordinates. This led to
showing the maximized window always on the first output.

This, along with the previous patch, fixes
https://bugs.freedesktop.org/show_bug.cgi?id=82967

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>
Reviewed-by: Pekka Paalanen <0f6ae7001e34c37b02fb2c1c2573ddf8f442136a@collabora.co.uk>

kwm81/weston,Gnurou/weston,xorgy/weston,giucam/weston,krezovic/weston,mchalupa/weston,giucam/weston,Tarnyko/weston-xdg_surface_present,Fantu/compositor-spice,kwm81/weston,eyolfson/weston,krezovic/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,jonnylamb/weston,Fantu/compositor-spice,Gnurou/weston,eyolfson/weston,sir-murray/weston,udoprog/weston,xorgy/weston,sir-murray/weston,udoprog/weston,jonnylamb/weston,mchalupa/weston