DisplaySettings: Add "Fonts" tab

This allows you to view, edit, and apply changes to the system fonts.

Userland/Applications/DisplaySettings/FontSettingsWidget.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/Widget.h>
+
+namespace DisplaySettings {
+
+class FontSettingsWidget : public GUI::Widget {
+    C_OBJECT(FontSettingsWidget);
+
+public:
+    virtual ~FontSettingsWidget() override;
+
+    void apply_settings();
+
+private:
+    FontSettingsWidget();
+};
+
+}