New lhcbid_v and lhcbids_field for SOACollection

This introduces an lhcbid_v type, a strong type based on int_v, and the corresponding lhcbids_field for the SOACollection. To be used to store and retrieve LHCbIDs in an SIMD way, and avoid implicit / accidental casts.

Also should be an example for similar fields in the future.

To do:

• Adapt all PrTrack classes with it, v3::Tracks to follow in its own MR.
• Add more functions to lhcbid_v, to make it similar to LHCbID (bit shifts etc are not provided for now, as I'd like to merge this soonish)

There are some not nice things in the pattern recognition algorithms, but they are connected to a deeper issues with the different proxies and how the information is stored and retrieved. It will not be addressed here or in Rec!2592 (merged).

Addresses #153 (closed)

Needs: Rec!2592 (merged)

@graven @gunther