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 patch changes all uses of GDK_DEPRECATED(_FOR) in gtk headers
by the versioned variants, GDK_DEPRECATED_IN_3_x(_FOR). At the same
time, we add GDK_AVAILABLE_IN_3_x annotations for all API additions
in 3.2 and 3.4.
This is the interface for GtkWidgets that can be associated with an
action on a GtkAppicationWindow or associated GtkApplication.
It essentially features 'action-name' and 'action-target' properties
with some associated convenience API.
This interface is implemented by GtkButton and GtkToolButton.
https://bugzilla.gnome.org/show_bug.cgi?id=667394
