gdk: Ensure surface buffer scale is set
GDK will only set the buffer scale for the surfaces it creates when attaching an image or when using an egl window window. Neither will happen for native clutter applications, thus directly set the buffer scale from clutter in that case (so it's in sync with the rendering scale)
Signed-off-by: Sjoerd Simons sjoerd@luon.net
https://bugzilla.gnome.org/show_bug.cgi?id=769190
We've been applying this in Debian since 2016.