LibWeb: Include cookies in form submission

Services expect cookies to be submitted with forms, especially login
screens.

Allows us to sign in to GitHub (including two factor authentication)
and start using it!

Userland/Libraries/LibWeb/HTML/HTMLFormElement.cpp

@@ -116,8 +116,7 @@ void HTMLFormElement::submit_form(RefPtr<HTMLElement> submitter, bool from_submi
         url.set_query(url_encode(parameters, AK::URL::PercentEncodeSet::ApplicationXWWWFormUrlencoded));
     }
 
-    LoadRequest request;
-    request.set_url(url);
+    LoadRequest request = LoadRequest::create_for_url_on_page(url, document().page());
 
     if (effective_method == "post") {
         auto body = url_encode(parameters, AK::URL::PercentEncodeSet::ApplicationXWWWFormUrlencoded).to_byte_buffer();