Enable access of a component of a vector field as a scalar field

The request here is to be able to grab the single component of a vector-valued field and treat it as a scalar, say to compute norms. I suppose this would be through the FiniteElementState representation of the field, but I'm not certain.

Start by locating the FiniteElementState representation referenced in the issue and trace how vector-valued fields are accessed. Determine the intended component-selection entry point and define a test showing that one component can be treated as a scalar for operations such as norm computation.

Written by the indexing model from the issue text.