Find the gobject.ParamSpec with the given name for an interface. Generally, the interface vtable passed in as g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().
any interface vtable for the interface, or the default vtable for the interface
name of a property to look up.
the gobject.ParamSpec for the property of the interface with the name property_name, or NULL if no such property exists.