Registers an additional interface for a type, whose interface lives in the given type plugin.
If the interface was already registered for the type in this plugin, nothing will be done.
As long as any instances of the type exist, the type plugin will not be unloaded.
Since 2.56 if this is null this will call
g_type_add_interface_static instead. This can be used when making a static build of the module.
| this | |
| instance_type |
type to which to add the interface. |
| interface_type |
interface type to add |
| interface_info |
type information structure |