Separate electronics IDs from detector IDs

[erik-wallin]

The ID given to an HGCROC Digi can now be either the electronics ID (that encodes the channel number) or the detector ID (that encodes the geometric position of the channel).

This is exemplified in HCalRawDecoder where a digi is given either the electronics ID or detector ID depending on whether there is a channel mapping available: https://github.com/LDMX-Software/Hcal/blob/c1076e713f3a1289f74a28118b19055c97aed1ce/src/Hcal/HcalRawDecoder.cxx#L650

Since these are two different concepts, we should make sure that they are never confused, somehow.