Add a framework similar to what we have for gtk reftests that lets us drop in a function to generate render nodes, and compare reference output.
We are officially switching to Meson as the default build system for GTK+.
This merged gtk, gdk and gsk into one library, making it possible to have internal private APIs between gtk them, as well as producing more efficient code. https://bugzilla.gnome.org/show_bug.cgi?id=773100
