wayland: Use scale from core wl_output protocol

wayland: Use scale from core wl_output protocol

The “xdg-output” protocol provides clients with the outputs size and
position in compositor coordinates, and does not provide the output
scale which is already provided by the core “wl_output” protocol.

So when receiving the wl_output scale event, we should update the scale
regardless of “xdg-output” support, otherwise the scale will remain to
its default value of 1 and the surface will be scaled up by the
compositor to match the actual output scale, which causes blurry fonts
and widgets.

Fixes: https://gitlab.gnome.org/GNOME/gtk/issues/1901
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>