Because of the previous awkward factoring of Origin we had two
implementations of Origin serializing and creation. Move the
implementation of DOMURL::url_origin into URL::origin, and
instead use the implemenation of URL::Origin::serialize for
serialization (replacing URL::serialize_origin).
This happens to fix 8 URL subtests as the two implemenations had
diverged, and URL::serialize_origin was previously missing the spec
changes of: whatwg/url@eee49fd and whatwg/url@fff33c3
While Origin is defined in the HTML spec - this leaves us with quite an
awkward relationship as the URL spec makes use of AO's from what is
defined in the HTML spec.
To simplify this factoring, relocate Origin into LibURL.
