GObject introspection does not currently support variadic methods. It
actually generates all the information Vala needs to do so, but it marks
the functions as introspectable="0", which is the same that happens when
"skip" annotation is added to the method. Therefore, in order to expose
these functions in Vala, we need a simple annotation to un-skip the
symbols.

References:
1. https://wiki.gnome.org/Projects/Vala/Bindings
2. https://gitlab.gnome.org/GNOME/vala/-/blob/main/vapi/metadata/Gtk-3.0.metadata