Introduce writeback connector screenshooter to DRM-backend
In this patch we add support to use writeback connectors to take screenshots in the DRM-backend. This will be the default screenshooter for the DRM-backend. The main reason why we need this is to be able to add plane composition tests to the CI.
Per screenshot Weston decides (based on hardware capacity) if it is going to use it or fallback to the GL-based screenshooter used by all the other backends. If the writeback screenshooter fails for some reason, it will fallback to the GL-based as well.
edit: removed, as it got outdated.
Here we have a document explaining how it works