Add new particle flow physics validation histograms.
requested to merge atlas-particleflow-software/athena:mhodgkin_updateNeutralPFlowHists_April2021 into master
This MR adds 3 new histograms for PFO and FE that split the pt spectrum into 3 pt bins. This was useful for further diagnostics of ATLPHYSVAL-741 and will be useful for future physics validation tasks as well.