eolian: start to express ownership transfere

eolian: start to express ownership transfere

before @owned was not even expressed in the api definitions of the
generated APIs, this adds support for it.

@owned is now expressed with EFL_TRANSFER_OWNERSHIP in a arguments. And
that preprocessor directive is documented.

Reviewed-by: Daniel Kolesa <daniel@octaforge.org>
Differential Revision: https://phab.enlightenment.org/D9369