Returns the GTypePlugin structure for the dynamic interface
interface_type which has been added to instance_type, or NULL if
interface_type has not been added to instance_type or does not
have a GTypePlugin structure. See g_type_add_interface_dynamic().
Returns the GTypePlugin structure for the dynamic interface interface_type which has been added to instance_type, or NULL if interface_type has not been added to instance_type or does not have a GTypePlugin structure. See g_type_add_interface_dynamic().