Function register_image_media_source 

pub fn register_image_media_source(registry: &MediaSourceRegistryHandle)

Register ImageFileMediaSource against the boot-time media registry.

Called from the host’s boot beside the registry’s creation. It lives here, with the mode, rather than in the host: the major and the producer that draws its buffers are one surface, and splitting them is how half of a mode ends up in the host.