flight_mode_manager: ManualAcceleration support weathervane yaw handler

- fixes https://github.com/PX4/PX4-Autopilot/issues/17911

src/modules/flight_mode_manager/tasks/ManualAcceleration/FlightTaskManualAcceleration.cpp

@@ -74,6 +74,18 @@ bool FlightTaskManualAcceleration::update()
 	_stick_acceleration_xy.getSetpoints(_position_setpoint, _velocity_setpoint, _acceleration_setpoint);
 
 	_constraints.want_takeoff = _checkTakeoff();
+
+	// check if an external yaw handler is active and if yes, let it update the yaw setpoints
+	if (_weathervane_yaw_handler && _weathervane_yaw_handler->is_active()) {
+		_yaw_setpoint = NAN;
+
+		// only enable the weathervane to change the yawrate when position lock is active (and thus the pos. sp. are NAN)
+		if (PX4_ISFINITE(_position_setpoint(0)) && PX4_ISFINITE(_position_setpoint(1))) {
+			// vehicle is steady
+			_yawspeed_setpoint += _weathervane_yaw_handler->get_weathervane_yawrate();
+		}
+	}
+
 	return ret;
 }
 

src/modules/flight_mode_manager/tasks/ManualAcceleration/FlightTaskManualAcceleration.hpp

@@ -52,10 +52,17 @@ public:
 	bool activate(const vehicle_local_position_setpoint_s &last_setpoint) override;
 	bool update() override;
 
+	/**
+	 * Sets an external yaw handler which can be used to implement a different yaw control strategy.
+	 */
+	void setYawHandler(WeatherVane *yaw_handler) override { _weathervane_yaw_handler = yaw_handler; }
+
 private:
 	StickAccelerationXY _stick_acceleration_xy;
 	StickYaw _stick_yaw;
 
 	void _ekfResetHandlerPositionXY() override;
 	void _ekfResetHandlerVelocityXY() override;
+
+	WeatherVane *_weathervane_yaw_handler{nullptr}; /**< external weathervane library, used to implement a yaw control law that turns the vehicle nose into the wind */
 };