Generate version and deprecation macros at build time

Generate version and deprecation macros at build time

Let's poach the same script used by GLib to avoid having to add all the
version macros by hand every time we increment the GTK version.

This is a work in progress:

- need to rename the GLIB_STATIC_COMPILATION check
- circular dependency: libgtkcss depends on gdkversionmacros.h, but libgdk
  depends on libgtkcss