Enforce centre-to-edge convention on the global indices of FT mat and sipm
There was a different convention between FTChannelID and monitoring code, e.g. https://gitlab.cern.ch/lhcb/Rec/-/blob/master/FT/FTMonitors/src/ClusterMonitor.h#L494
This MR enforces the globalMatIdx and globalSiPMIdx to be in centre-to-edge convention.