Allow Fields whose Type is a Flag Enumeration to be Stored as Relations

[justin-millman]

I don't think that the current features in either the Extraction or Reconstitution space are sufficient to support flag-enumeration-type Fields that are to be stored as a Relation. (I don't even think there's a way right now to indicate that they should be.)

• Indication is straightforward: Just add a new annotation
• How do we deal with inserts vs. deletes vs. saves on Extraction, given that we won't have the tracking that comes from an IRelation?
• How do we do Reconstitution, given that we won't be able to Repopulate like we can with an IRelation?
• Do data conversions apply to the individual flags? I think the answer is yes: the Field gets treated as if it were a RelationList<EnumT>, so any data conversion (e.g. [Numeric] or to-string as default or custom converter annotation) would get applied to the items in the Relation, just like with any other Relation.

Important Question: Should Relation-style be the default for such Fields, with an opt-out?