QB: Allow constraining fields without adding to view

Currently you can only constrain fields that have been added to the view. In the JSP webapp, it was possible to constrain fields without adding them to the view. We lost a feature!

Thanks to @sergiocontrino for spotting this.

Start in the webapp's query-builder constraint handling and compare the current behavior with the JSP webapp behavior described in the issue. Done means a field can be constrained without being added to the view, with coverage confirming that both displayed and non-displayed fields work.

Written by the indexing model from the issue text.