Consider use of Flight POJOs instead of protobufs

[devinrsmith]

While implementing #5339, I wished I could have used the Flight POJOs (org.apache.arrow.flight) everywhere instead of the Flight protobufs (org.apache.arrow.flight.impl); while it would be a breaking change, it would be relatively straightforward to update all of our code save for the grpc sending layer, to work directly with Flight POJOs.

For example, io.deephaven.server.session.ActionResolver was implemented with org.apache.arrow.flight.Action, org.apache.arrow.flight.ActionType, and org.apache.arrow.flight.Result as opposed to org.apache.arrow.flight.impl.Flight.Action, org.apache.arrow.flight.impl.Flight.ActionType, and org.apache.arrow.flight.impl.Flight.Result.