Multi-EKF support (ekf2)

- ekf2 can now run in multi-instance mode (currently up to 9 instances)
    - in multi mode all estimates are published to alternate topics (eg estimator_attitude instead of vehicle_attitude)
 - new ekf2 selector runs in multi-instance mode to monitor and compare all instances, selecting a primary (eg N x estimator_attitude => vehicle_attitude)
 - sensors module accel & gyro inconsistency checks are now relative to the mean of all instances, rather than the current primary (when active ekf2 selector is responsible for choosing primary accel & gyro)
 - existing consumers of estimator_status must check estimator_selector_status to select current primary instance status
 - ekf2 single instance mode is still fully supported and the default

Co-authored-by: Paul Riseborough <gncsolns@gmail.com>

src/modules/simulator/simulator.h

@@ -143,6 +143,8 @@ private:
 			delete _dist_pubs[i];
 		}
 
+		px4_lockstep_unregister_component(_lockstep_component);
+
 		_instance = nullptr;
 	}
 
@@ -288,6 +290,8 @@ private:
 	px4::atomic<bool> _has_initialized {false};
 #endif
 
+	int _lockstep_component{-1};
+
 	DEFINE_PARAMETERS(
 		(ParamInt<px4::params::MAV_TYPE>) _param_mav_type,
 		(ParamInt<px4::params::MAV_SYS_ID>) _param_mav_sys_id,