- ensure surface writing is time-step and nFields aware.
  This avoids overwriting (ignoring) previous output fields.

- allow sampled surfaces to be used for weight fields as well.
  Not sure why this restriction was still there.

- remove old compatibility reading of orientedFields.
  Last used in v1612, now removed.

- only use face sampling. For surfaceFieldValue we can only do
  something meaningful with face values.

ENH: modify interface methods for surfaceWriter

- replace direct modification of values with setter methods.
  Eg,
     old: writer.isPointData() = true;
     new: writer.isPointData(true);

  This makes it possible to add internal hooks to catch state changes.

ENH: allow post-construction change to sampledSurface interpolation

- rename interpolate() method to isPointData() for consistency with
  other classes and to indicate that it is a query.

- additional isPointData(bool) setter method to change the expected
  represent...