land_detector: treat altitude mode like position mode with vertical checks but without horizontal checks

because in altitude mode we have a baro available and can therefore check vertical movement
we can not check horizontal movement but I consider the checks for landing still pretty safe
unlike in manual mode we are not allowed to disarm before land detection in altitude mode

src/modules/land_detector/MulticopterLandDetector.h

@@ -135,6 +135,7 @@ private:
 
 	/* get control mode dependent pilot throttle threshold with which we should quit landed state and take off */
 	float _get_takeoff_throttle();
+	bool _has_altitude_lock();
 	bool _has_position_lock();
 	bool _has_manual_control_present();
 	bool _has_minimal_thrust();