DisplaySettings: Add an Effects tab

Effects tab provides the UI for setting SystemEffects.
DisplaySettings is getting a bit crowded and might need a re-org
at some point, but this seems like a good home for effects while
the settings mature.

Userland/Applications/DisplaySettings/EffectsSettingsWidget.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/SettingsWindow.h>
+#include <LibGUI/SystemEffects.h>
+
+namespace GUI {
+
+namespace DisplaySettings {
+
+class EffectsSettingsWidget final : public SettingsWindow::Tab {
+    C_OBJECT(EffectsSettingsWidget);
+
+public:
+    virtual ~EffectsSettingsWidget() override = default;
+
+    virtual void apply_settings() override;
+
+private:
+    EffectsSettingsWidget();
+
+    ErrorOr<void> load_settings();
+
+    SystemEffects m_system_effects;
+    Vector<String> m_geometry_list;
+    RefPtr<ComboBox> m_geometry_combobox;
+};
+
+}
+
+}