Add custom Render sample

[avaloniaui]

Add custom Render sample

[maxkatz6]

In general, we need samples for these different approaches:

1. WriteableBitmap rendering (poor performance and quality, but easy caching and flexibility). WriteableBitmapPage
2. Render method override with Draw commands (DrawRectanle...). CustomDrawingExampleControl
3. ICustomDrawOperation - render thread rendering, direct drawing to the canvas. Can access SkiaSharp canvas. CustomSkiaPage
4. Composition API custom visual CompositionCustomVisualHandler
5. GPU interop - hardcore approach, the best for low level rendering with direct access to OpenGL/D3D/Vulkan. Should be ideal for media players or game integrations. GpuInterop OpenGl

We have samples for all of these approaches randomly scattered across our repositories. At the very least this comment should help with googling them. Ideally, yes, these should be duplicated here.

• On how to force next rendered frame (Dispatcher + InvalidateVisual in 0.10, and Window.RequestAnimationFrame in 11.0)
• On how to render text efficiently (can be yet another series of samples, as there are many approaches again)