LibWeb: Add getter to NavigationDestination to get its URL as an AK::URL

Other parts of LibWeb are going to want to mess with the URL object, not
its serialzied representation. So let's add a backdoor getter.

Userland/Libraries/LibWeb/HTML/NavigationDestination.h

@@ -37,6 +37,8 @@ public:
 
     virtual ~NavigationDestination() override;
 
+    AK::URL const& raw_url() const { return m_url; }
+
 private:
     NavigationDestination(JS::Realm&);