Canvas redraw is slow for large primitive draw-command workloads

Large Canvas Paint handlers that issue thousands of primitive drawing calls can repaint slowly during resize or other full redraws. A simple 10x10 grid with 1 point gaps can produce tens of thousands of Graphics.FillRectangle calls on large canvases, causing visible redraw lag on some machines.

Expected behaviour: Canvas redraws should remain responsive for reasonable static drawing workloads, or the runtime should avoid unnecessary repeated replay overhead where possible.