Browser: Add support for CookieJar to run in a transient, in-memory mode

This is to allow running Ladybird without the SQL database for testing.
Primarily, this will let us set 'follow-fork-mode' to 'child' within GDB
to enter the WebContent process, rather than the SQLServer process. But
this is also handy for digging into cookie storage issues.

Userland/Applications/Browser/Forward.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Traits.h>
+
+namespace Browser {
+
+class CookieJar;
+class Database;
+
+struct CookieStorageKey;
+
+}
+
+namespace AK {
+
+template<>
+struct Traits<Browser::CookieStorageKey>;
+
+}