We previously used an empty optional to denote that a ReferrerPolicy is
in the default empty string state. However, later additions added an
explicit EmptyString state. This patch moves all users to the explicit
state, and stops using `Optional<ReferrerPolicy>` everywhere except for
when an option not being passed from JavaScript has meaning.
Along with putting functions in the URL namespace into a DOMURL
namespace.
This is done as LibWeb is in an awkward situation where it needs
two URL classes. AK::URL is the general purpose URL class which
is all that is needed in 95% of cases. URL in the Web namespace
is needed predominantly for interfacing with the javascript
interfaces.
Because of two URLs in the same namespace, AK::URL has had to be
used throughout LibWeb. If we move AK::URL into a URL namespace,
this becomes more painful - where ::URL::URL is required to
specify the constructor (and something like
::URL::create_with_url_or_path in other places).
To fix this problem - rename the class in LibWeb implementing the
URL IDL interface to DOMURL, along with moving the other Web URL
related classes into this DOMURL folder.
One could argue that this name also makes the situation a little
more clear in LibWeb for why these two URL classes need be used
in the first place.
