Demos: Create demo for VirGL gpu device

This is a simple demo for VirGL, that does the bare minimum required to
create and render a spinning cube (with one color per face).

Userland/Demos/VirGLDemo/Widget.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2022, Sahan Fernando <sahan.h.fernando@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGUI/Widget.h>
+
+void update_frame(RefPtr<Gfx::Bitmap>, unsigned num_cycles);
+
+constexpr size_t DRAWTARGET_WIDTH = 500;
+constexpr size_t DRAWTARGET_HEIGHT = 500;
+
+class Demo final : public GUI::Widget {
+    C_OBJECT(Demo)
+public:
+    virtual ~Demo() override;
+    bool show_window_frame() const { return m_show_window_frame; }
+
+    Function<void(GUI::ContextMenuEvent&)> on_context_menu_request;
+
+protected:
+    virtual void context_menu_event(GUI::ContextMenuEvent& event) override
+    {
+        if (on_context_menu_request)
+            on_context_menu_request(event);
+    }
+
+private:
+    Demo();
+
+    RefPtr<Gfx::Bitmap> m_bitmap;
+
+    virtual void paint_event(GUI::PaintEvent&) override;
+    virtual void timer_event(Core::TimerEvent&) override;
+
+    int m_cycles;
+    bool m_show_window_frame { true };
+};