Break up Cluster::clusterShape into named fields

[veprbl]

The clusterShape vector member had become a dumping ground for additional values that bypass EDM review procedure

EDM4eic/edm4eic.yaml

Line 292 in f21b388

- float shapeParameters // Should be set in metadata, for now it's a list of -- radius [mm], dispersion [mm], 2 entries for theta-phi widths [rad], 3 entries for x-y-z widths [mm].

In addition to that, accessing values by index is confusing to our users. We should migrate away from this approach.

See also eic/EICrecon#1511

[ruse-traveler]

I'd like to second this: it's a bit embarrassing, but I keep forgetting we have this information stored 😓