This is a neat trick to get around the circularity between GDK, GSK and
GTK that we inherit with the GdkPaintable interface.

GdkPaintable uses GtkSnapshot
GtkSnapshot creates GskRenderNodes
GskRenderNodes use GdkTextures
GdkTexture will soon implement GdkPaintable

This causes a loop that spans GDK, GSK and GTK and this is the easiest
way to resolve it without breaking bindings (at least that's the idea).