Handle resolution changes in the GDK backend code

gdk_x11_display_set_window_scale() affects the interpretation of the
Xft/DPI XSETTING - it is substituted inside GDK with the value of
Gdk/UnscaledDPI xsetting. However, this change is not propagated to
GTK+ and from GTK+ back to gdk_screen_set_resolution() until the
main loop is run.

Fix this by handling the screen resolution directly in gdk/x11.
This requires duplication of code between GDK and GTK+ since we still
have to handle DPI in GTK+ in the case that GdkSettings:gtk-xft-dpi
is set by the application.

https://bugzilla.gnome.org/show_bug.cgi?id=733076

gdk/quartz/gdkscreen-quartz.c

@@ -75,8 +75,8 @@ gdk_quartz_screen_init (GdkQuartzScreen *quartz_screen)
   NSScreen *nsscreen;
 
   nsscreen = [[NSScreen screens] objectAtIndex:0];
-  gdk_screen_set_resolution (screen,
-                             72.0 * [nsscreen userSpaceScaleFactor]);
+  _gdk_screen_set_resolution (screen,
+                              72.0 * [nsscreen userSpaceScaleFactor]);
 
   gdk_quartz_screen_calculate_layout (quartz_screen);