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.
When the $(resource_prefix)/gtk/help-overlay.ui resource exists,
load a GtkShortcutsWindow from it for each GtkApplicationWindow,
and set up a win.show-help-overlay action with accels <Primary>F1
and <Primary>? to show it.
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 a GtkWindow subclass that "application windows" will use. Each
is associated with a GtkApplication, has the ability to show menus and
will have its own associated set of actions.