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/CMakeLists.txt

@@ -0,0 +1,13 @@
+serenity_component(
+    VirGLDemo
+    TARGETS VirGLDemo
+)
+
+set(SOURCES
+    CommandBufferBuilder.cpp
+    VirGLDemo.cpp
+    Widget.cpp
+)
+
+serenity_app(VirGLDemo ICON app-cube)
+target_link_libraries(VirGLDemo LibMain LibGUI)