DFV: allow the data collection for Pick fields to be dynamically replaced

[pglewis]

[pglewis]

PR: #5048

[pglewis]

Without some sort of custom processing on submit the most you can really do is provide a subset of the data with valid IDs for the related items. I'm gonna hold on the PR above for the moment since some filtering methods on the pick field's collection is a more generally useful way to provide the functionality.