This consolidates the two separate `CGImage`s (`colorImage` and `shapeImage`) previously used in `WineContentView` into a single `IOSurface` that also holds the window mask information in its alpha channel now.
The alpha channel is now being updated in `macdrv_surface_flush`, whenever the shape changes (and stores that change for the next update, to also keep the front buffer in sync).
This reduces the delay from setting a `CGImage` to a layer from 50ms to about 1.5ms in the `IOSurface` case (also accounting for `vImageSelectChannels_ARGB8888` operation).
Based on a patch by @bshanks.
I am already putting it out for feedback, but I will so some more testing to see how the performance impact of this is and do more exhaustive testing with shaped windows.
Ideally the double buffer solution can be avoided as well... Also the `HBITMAP` for the windows is currently backed by a `CGDataProviderRef` and could also become an `IOSurface` I believe.