LibDevTools: Introduce a Firefox DevTools server library

To aid with debugging web page issues in Ladybird without needing to
implement a fully fledged inspector, we can implement the Firefox
DevTools protocol and use their DevTools. The protocol is described
here:

https://firefox-source-docs.mozilla.org/devtools/backend/protocol.html

This commit contains just enough to connect to Ladybird from a DevTools
client.

Libraries/LibDevTools/Connection.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/Function.h>
+#include <AK/NonnullOwnPtr.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <LibCore/Socket.h>
+#include <LibDevTools/Forward.h>
+
+namespace DevTools {
+
+class Connection : public RefCounted<Connection> {
+public:
+    static NonnullRefPtr<Connection> create(NonnullOwnPtr<Core::BufferedTCPSocket>);
+    ~Connection();
+
+    Function<void()> on_connection_closed;
+    Function<void(JsonObject const&)> on_message_received;
+
+    void send_message(JsonValue const&);
+
+private:
+    explicit Connection(NonnullOwnPtr<Core::BufferedTCPSocket>);
+
+    ErrorOr<void> on_ready_to_read();
+    ErrorOr<JsonValue> read_message();
+
+    NonnullOwnPtr<Core::BufferedTCPSocket> m_socket;
+};
+
+}