LibWeb: Re-implement HTML::Navigator using IDL

Get rid of the bespoke NavigatorObject class and use the modern IDL
strategies for creating platform objects to re-implement Navigator and
its associcated mixin interfaces. While we're here, implement it in a
way that brings WorkerNavigator up to spec :^)

Userland/Libraries/LibWeb/HTML/NavigatorLanguage.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2022, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+namespace Web::HTML {
+
+class NavigatorLanguageMixin {
+public:
+    // https://html.spec.whatwg.org/multipage/system-state.html#dom-navigator-language
+    String language() const { return m_current_preferred_languages[0]; }
+
+    // https://html.spec.whatwg.org/multipage/system-state.html#dom-navigator-languages
+    // FIXME: The same object must be returned until the user agent needs to return different values, or values in a
+    //        different order.
+    Vector<String> languages() const { return m_current_preferred_languages; }
+
+protected:
+    Vector<String> m_current_preferred_languages = { "en-US" };
+};
+
+}