LibWeb: Add facilities to serialize EnvironmentSettingsObjects

This will be used to transfer information about the parent context to
DedicatedWorkers and future out-of-process Worker/Worklet
implementations for fetching purposes. In order to properly check
same-origin and other policies, we need to know more about the outside
settings than we were previously passing to the WebWorker process.

Userland/Libraries/LibWeb/HTML/PolicyContainers.cpp

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2024, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibIPC/Decoder.h>
+#include <LibIPC/Encoder.h>
+#include <LibWeb/HTML/PolicyContainers.h>
+
+namespace IPC {
+
+template<>
+ErrorOr<void> encode(IPC::Encoder& encoder, Web::HTML::PolicyContainer const& policy_container)
+{
+    TRY(encode(encoder, policy_container.referrer_policy));
+
+    return {};
+}
+
+template<>
+ErrorOr<Web::HTML::PolicyContainer> decode(IPC::Decoder& decoder)
+{
+    auto referrer_policy = TRY(decoder.decode<Web::ReferrerPolicy::ReferrerPolicy>());
+
+    return Web::HTML::PolicyContainer { .referrer_policy = referrer_policy };
+}
+
+}