We use a compilation symbol in our build to allow the inclusion of
specific headers while building GTK, to avoid the need to include only
the global header.
Each namespace has its own compilation symbol because we used to have
different libraries, and strict symbol visibility between libraries;
now that we have a single library, and we can use private symbols across
namespaces while building GTK, we should have a single compilation
symbol, and simplify the build rules.
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.
