Renaming ItemFactory<T> to GenericFactory<T>.
Prefix "item" is too narrow as for the name of factory<T> class.
factory<T> can be used not only the items, also for content widgets
such as radio, check, image, button, which can expose it's property
in the factory by Extensions and introspection.
change the perfix "item" to "Generic" as generic widget factory with
GenericType in mono Efl.Ui.
Depends on D11160