add Android app skeleton

GitOrigin-RevId: 35018deaba

Jumpy.Shared/JumpyGame.cs

@@ -24,6 +24,10 @@ namespace Jumpy {
       display = (IDisplay) Services.GetService(typeof(IDisplay));
       display.Initialize(Window, graphics);
       display.SetFullScreen(fullScreen);
+      // TODO: something like this for mobile devices?
+      // graphics.SupportedOrientations =
+      //     DisplayOrientation.LandscapeLeft | DisplayOrientation.LandscapeRight;
+
       base.Initialize();
     }