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.
This adds support to the GDK Win32 backend so that we can support Vulkan
context creation for use in the GSK Vulkan renderer, so that we can test
it on Windows platforms as well.
https://bugzilla.gnome.org/show_bug.cgi?id=776544