Navigator: Support straight line mission landings (#23576)

* introduced altitude acceptance radius in position setpoint for fixed
wing guidance
- allows navigator to explicitly set the altitude acceptance radius
- needed for staright line landing support

* added ignore_alt_acceptance to position setpoint message to allow guidance
logic to ignore altitude error on waypoint
- can be useful to prevent loitering at a waypoint within a mission landing sequence

* only set altitude acceptance radius to infinity for a waypoint inside a mission landing
for fixed wing vehicles

* navigator: return altitude acceptance radius from triplet if it's valid

* FixedWingPositionControl: check if alt acceptance radius provided in position setpoint
is larger 0

---------

Signed-off-by: RomanBapst <bapstroman@gmail.com>
Co-authored-by: Alvaro Fernandez <alvaro@auterion.com>

src/modules/fw_pos_control/FixedwingPositionControl.cpp

@@ -1029,11 +1029,15 @@ FixedwingPositionControl::handle_setpoint_type(const position_setpoint_s &pos_sp
 					   _current_latitude, _current_longitude, _current_altitude,
 					   &dist_xy, &dist_z);
 
+		const float acc_rad_z = (PX4_ISFINITE(pos_sp_curr.alt_acceptance_radius)
+					 && pos_sp_curr.alt_acceptance_radius > FLT_EPSILON) ? pos_sp_curr.alt_acceptance_radius :
+					_param_nav_fw_alt_rad.get();
+
 		// Achieve position setpoint altitude via loiter when laterally close to WP.
 		// Detect if system has switchted into a Loiter before (check _position_sp_type), and in that
 		// case remove the dist_xy check (not switch out of Loiter until altitude is reached).
 		if ((!_vehicle_status.in_transition_mode) && (dist >= 0.f)
-		    && (dist_z > _param_nav_fw_alt_rad.get())
+		    && (dist_z > acc_rad_z)
 		    && (dist_xy < acc_rad || _position_sp_type == position_setpoint_s::SETPOINT_TYPE_LOITER)) {
 
 			// SETPOINT_TYPE_POSITION -> SETPOINT_TYPE_LOITER