Add pivot offset for rotations.

DaggerFramework/Source/SceneGraph/Entities/RectangleShape2d.cs

@@ -9,6 +9,7 @@ public class RectangleShape2d : Drawable2d
     public Color Color { get; set; } = Color.White;
     public override void OnDraw(Renderer renderer)
     {
+        PivotOffset = Size / 2;
         renderer.DrawRectangle(Size, Color);
     }
 }