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/Actors/DeviceActor.cpp

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/JsonObject.h>
+#include <AK/String.h>
+#include <LibCore/Version.h>
+#include <LibDevTools/Actors/DeviceActor.h>
+#include <LibWeb/Loader/UserAgent.h>
+
+namespace DevTools {
+
+NonnullRefPtr<DeviceActor> DeviceActor::create(DevToolsServer& devtools, ByteString name)
+{
+    return adopt_ref(*new DeviceActor(devtools, move(name)));
+}
+
+DeviceActor::DeviceActor(DevToolsServer& devtools, ByteString name)
+    : Actor(devtools, move(name))
+{
+}
+
+DeviceActor::~DeviceActor() = default;
+
+void DeviceActor::handle_message(StringView type, JsonObject const&)
+{
+    if (type == "getDescription"sv) {
+        auto build_id = Core::Version::read_long_version_string().to_byte_string();
+
+        // https://github.com/mozilla/gecko-dev/blob/master/devtools/shared/system.js
+        JsonObject value;
+        value.set("apptype"sv, "ladybird"sv);
+        value.set("name"sv, BROWSER_NAME);
+        value.set("brandName"sv, BROWSER_NAME);
+        value.set("version"sv, BROWSER_VERSION);
+        value.set("appbuildid"sv, build_id);
+        value.set("platformbuildid"sv, build_id);
+        value.set("platformversion"sv, "135.0"sv);
+        value.set("useragent"sv, Web::default_user_agent);
+        value.set("os"sv, OS_STRING);
+        value.set("arch"sv, CPU_STRING);
+
+        JsonObject response;
+        response.set("from"sv, name());
+        response.set("value"sv, move(value));
+
+        send_message(move(response));
+        return;
+    }
+
+    send_unrecognized_packet_type_error(type);
+}
+
+}