Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.
gdk_window_create_vulkan_context() now exists and will return a Vulkan
context for the given window. It even initializes the surface. But it
doesn't do anything useful yet.
Adds the gdk_display_ref_vulkan() and gdk_display_unref_vulkan()
functions which setup/tear down VUlkan support for the display.
Nothing is using those functions yet.
