I would like to understand how to pack and unpack raw mavlink messages from mavros's mavlink/to and mavlink/from topics (outside of a mavros plugin).
I know there exists a function to convert mavlink_message_t structs to the mavros_msgs::Mavlink object, but (with a new version of mavros?) it is unclear how to convert from specific mavlink message types to mavlink_message_t from a specific message type. I have done this previously by just using the mavlink c-types, for example, just by including mavros/utils
// ... fill in message fields
mavlink_msg_mission_item_encode(255, 1, &packet, &waypoint_msg);
But now those types are no longer available? I see in the mavros source code that the specific message types are represented as subclasses of a mavlink::Message base class (e.g. mavlink::common::msg::MISSION_ITEM), but I do not see methods to pack/unpack them. My attempts to compile while including the underlying mavlink headers have all failed so far.