Use position of InDet::SCT_Cluster when converting strip cluster to xAOD EDM
The InDet->xAOD converter for strip uses the clusterId to fetch the cluster position but using polar coordinates when the cluster is from an endcap disk. In SCT_ClusteringTool, the clusterId is set from the SiCellId of the first strip in the cluster (and in general is not 100% garanteed to correspond to the central strip), therefore the computed position can be biased when the cluster comprises more than a single strip. This simple MR fetches the SiCellId using the cartesian position already stored in the InDet cluster.
The effect is very small, but this eliminates one potential source of discrepancy with the native xAOD strip clustering which is in development in !56716 (merged).