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
(cherry picked from commit 501f92b54eee7bcf7b60621aa4238fcbdc610d99;
amended to add leading whitespace to expectation due to serenity not
yet having LadybirdBrowser/ladybird#1603)
