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/sensors/vehicle_angular_velocity/VehicleAngularVelocity.cpp

@@ -68,7 +68,8 @@ bool VehicleAngularVelocity::Start()
 	}
 
 	if (!SensorSelectionUpdate(true)) {
-		ScheduleDelayed(10_ms);
+		_selected_sensor_sub_index = 0;
+		_sensor_sub.registerCallback();
 	}
 
 	return true;
@@ -157,6 +158,15 @@ void VehicleAngularVelocity::CheckFilters()
 
 void VehicleAngularVelocity::SensorBiasUpdate(bool force)
 {
+	// find corresponding estimated sensor bias
+	if (_estimator_selector_status_sub.updated()) {
+		estimator_selector_status_s estimator_selector_status;
+
+		if (_estimator_selector_status_sub.copy(&estimator_selector_status)) {
+			_estimator_sensor_bias_sub.ChangeInstance(estimator_selector_status.primary_instance);
+		}
+	}
+
 	if (_estimator_sensor_bias_sub.updated() || force) {
 		estimator_sensor_bias_s bias;
 
@@ -321,6 +331,7 @@ void VehicleAngularVelocity::PrintStatus()
 	PX4_INFO("selected sensor: %d (%d), rate: %.1f Hz",
 		 _selected_sensor_device_id, _selected_sensor_sub_index, (double)_update_rate_hz);
 	PX4_INFO("estimated bias: [%.4f %.4f %.4f]", (double)_bias(0), (double)_bias(1), (double)_bias(2));
+
 	_calibration.PrintStatus();
 }