Gets the zorder of the accessible. The value G_MININT will be returned
if the layer of the accessible is not ATK_LAYER_MDI.
WARNING: atk_object_get_mdi_zorder is deprecated and should not be used in newly-written code. Use atk_component_get_mdi_zorder instead.
[integer] a gint which is the zorder of the accessible, i.e. the depth at
which the component is shown in relation to other components in the same
container.