LibWeb: Add the URLSearchParams built-in

This is a very partial implementation, as some features (like 2 of the
possible constructor types, iteration and the getAll method) are
missing, and other's are not implemented due to the currently missing
URL built-in.

Userland/Libraries/LibWeb/URL/URLSearchParams.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Bindings/Wrappable.h>
+#include <LibWeb/DOM/ExceptionOr.h>
+#include <LibWeb/URL/URL.h>
+
+namespace Web::URL {
+
+class URLSearchParams : public Bindings::Wrappable
+    , public RefCounted<URLSearchParams> {
+public:
+    using WrapperType = Bindings::URLSearchParamsWrapper;
+
+    static NonnullRefPtr<URLSearchParams> create(Vector<QueryParam> list)
+    {
+        return adopt_ref(*new URLSearchParams(move(list)));
+    }
+
+    static DOM::ExceptionOr<NonnullRefPtr<URLSearchParams>> create_with_global_object(Bindings::WindowObject&, const String& init);
+
+    void append(String const& name, String const& value);
+    void delete_(String const& name);
+    String get(String const& name);
+    bool has(String const& name);
+    void set(String const& name, String const& value);
+
+    void sort();
+
+    String to_string();
+
+private:
+    explicit URLSearchParams(Vector<QueryParam> list)
+        : m_list(move(list)) {};
+
+    void update();
+
+    Vector<QueryParam> m_list;
+};
+
+}