Function glib::subclass::types::register_type

pub fn register_type<T: ObjectSubclass>() -> Type where
    <<T as ObjectSubclass>::ParentType as ObjectType>::RustClassType: IsSubclassable<T>, 

Register a glib::Type ID for T.

This must be called only once and will panic on a second call.

The glib_object_subclass! macro will create a get_type() function around this, which will ensure that it's only ever called once.