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/modules/mc_pos_control/Utility/ControlMath.cpp

@@ -103,7 +103,7 @@ vehicle_attitude_setpoint_s thrustToAttitude(const Vector3f &thr_sp, const float
 	Eulerf euler = R_sp;
 	att_sp.roll_body = euler(0);
 	att_sp.pitch_body = euler(1);
-	att_sp.thrust = thr_sp.length();
+	att_sp.thrust_body[2] = -thr_sp.length();
 
 	return att_sp;
 }

src/modules/mc_pos_control/mc_pos_control_main.cpp

@@ -827,7 +827,7 @@ MulticopterPositionControl::run()
 			matrix::Quatf q_sp = matrix::Eulerf(_att_sp.roll_body, _att_sp.pitch_body, _att_sp.yaw_body);
 			q_sp.copyTo(_att_sp.q_d);
 			_att_sp.q_d_valid = true;
-			_att_sp.thrust = 0.0f;
+			_att_sp.thrust_body[2] = 0.0f;
 		}
 	}