VTOL rate control architecture improvements (#10819)

* attitude and rate setpoint message: use 3D array for thrust demand
* FixedWingAttitudeControl: rework airspeed scaling
  * move airspeed and scaling calculation into separate method
  * if vtol in hover and airspeed disabled use minimum airspeed instead of trim airspeed

src/examples/rover_steering_control/main.cpp

@@ -182,7 +182,7 @@ void control_attitude(const struct vehicle_attitude_setpoint_s *att_sp, const st
 	actuators->control[2] = yaw_err * pp.yaw_p;
 
 	/* copy throttle */
-	actuators->control[3] = att_sp->thrust;
+	actuators->control[3] = att_sp->thrust_body[0];
 
 	actuators->timestamp = hrt_absolute_time();
 }