CanvasSwapChain should expose buffer as CanvasRenderTarget

[lukasf]

I wonder why the CancasSwapChain only allows directly creating a drawing session on the buffer. Internally, it creates a ID2D1Bitmap1, which is the equivalent of a CanvasRenderTarget, but the it immediately creates a CanvasDrawingSession from it and returns it.

As an alternative, I think it would be good to also allow getting the buffer as CanvasRenderTarget. Then it would be possible to use interop for accessing the underlying texture and directly rendering to it using d3d or d2d, opening up usage of CancasSwapChain in a lot of other, interop based scenarios.

Are there any opinion on this? I am a bit surprised that this is not yet available.