Add new custom mavlink message for 3.6

Let’s see on guide. First, second, third and fourth steps are easy. I just add message in ardupilotmega.xml and build ardupilot.

I want to receive message from GCS and send it via gcs().send_text. First problem. commands_logic.cpp is not exist. Secondly, where should I read and send messages? In my opinion, in GCS_MAVLINK_Copter messages are sent to GCS from ardupilot(I say about mavlink message not gcs().send_text). May ardupilot/libraries/GCS_MAVLink/ is better way for adding custom message?

I see a few classes in ArduCopter/GCS_Mavlink.cpp “Copter” and “GCS_MAVLINK_Copter”. Which the defferent between it? For example, function from Copter don’t use in code(github search don’t find it Copter::send_nav_controller_output()).