LibWeb: Add the Web::URL namespace and move URLEncoder to it

This namespace will be used for all interfaces defined in the URL
specification, like URL and URLSearchParams.

This has the unfortunate side-effect of requiring us to use the fully
qualified AK::URL name whenever we want to refer to the AK class, so
this commit also fixes all such references.

Userland/Libraries/LibWeb/URL/URL.h

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+namespace Web::URL {
+
+struct QueryParam {
+    String name;
+    String value;
+};
+String url_encode(const Vector<QueryParam>&, AK::URL::PercentEncodeSet);
+
+}