SoA SciFiTracker hit class and adapted PrForwardTracking

RTA WP2 Directions

This MR improves the throughput of the PrForwardTracking in HLT2 by

• combining the AoS hit class PrHit.h and its handler FTHitHandler.h into a (mostly) SoA replacement PrSciFiHits.h
• adapting ForwardTracking accordingly
• simplifying and improving code where possible

The PrSciFiHits class and its storing algorithm PrStoreSciFiHits.cpp are very similar to the ones used in the SciFiTrackForwarding, but contain more information about the hit. The ForwardTracking gains

• ~+13% throughput
• same efficiency

Consequences:

• effect on the throughput of the HLT2 reconstruction will be small 🤷
• HLT1 baseline is not affected
• for now both PrStoreSciFiHits.cpp and PrStoreFTHit.cpp run in HLT2 with negligible effect

@sstahl @decianm @chasse

Merge together with Moore!345 (merged) and Brunel!941 (merged)

Needs a reference update in Brunel (and maybe Moore because of RICH histos).