Reintroduce super-pixel demosaicing
The "super-pixel" demosaicing was removed when we started using librtprocess for demosaicing instead of Siril functions. It has the particularity of changing image dimensions: for a Bayer matrix, only one pixel of each color is kept, so it divides by two width and height.
Advantages: it does not use interpolation, it is fast, it lowers the noise on the green channel because two photosites are averaged Drawbacks: some resolution is lost, works only with Bayer filtered sensors, handling image size change in the code adds complexity.