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/navigator/rtl_direct_mission_land.cpp

@@ -212,6 +212,13 @@ void RtlDirectMissionLand::setActiveMissionItems()
 		}
 
 		mission_item_to_position_setpoint(_mission_item, &pos_sp_triplet->current);
+
+		// prevent lateral guidance from loitering at a waypoint as part of a mission landing if the altitude
+		// is not achieved.
+		if (_vehicle_status_sub.get().vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING && MissionBase::isLanding()
+		    && _mission_item.nav_cmd == NAV_CMD_WAYPOINT) {
+			pos_sp_triplet->current.alt_acceptance_radius = FLT_MAX;
+		}
 	}
 
 	issue_command(_mission_item);