ClockSettings: Add a GUI application to set the system time zone

This application can be expanded with other clock-related options. For
an initial iteration, it has just an option to change the time zone.

Userland/Applications/ClockSettings/ClockSettingsWidget.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2022, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/RefPtr.h>
+#include <AK/String.h>
+#include <LibGUI/SettingsWindow.h>
+#include <LibGUI/TextEditor.h>
+#include <LibGUI/Window.h>
+
+class ClockSettingsWidget final : public GUI::SettingsWindow::Tab {
+    C_OBJECT(ClockSettingsWidget)
+
+private:
+    ClockSettingsWidget();
+
+    virtual void apply_settings() override;
+    virtual void reset_default_values() override;
+    void set_time_zone() const;
+
+    String m_time_zone;
+    RefPtr<GUI::ComboBox> m_time_zone_combo_box;
+};