Add support to extract .dmg volumes
Add support to extract .dmg volumes

Part-of: <https://gitlab.freedesktop.org/gstreamer/cerbero/-/merge_requests/661>

GStreamer/cerbero,GStreamer/cerbero,nirbheek/cerbero,GStreamer/cerbero,nirbheek/cerbero,nirbheek/cerbero,GStreamer/cerbero,nirbheek/cerbero,GStreamer/cerbero