Integrate prismatic Lagrange elements into filters.

Make the dataset surface and unstructured-grid geometry filters
process Lagrange elements properly.
Note that the unstructured-grid geometry filter does not handle
arbitrary-order elements; because it has a hardcoded maximum
number of points for indexing "surfels" (bounding surfaces of
3-d cells), it can handle at most order 4 quadrilaterals.

This also fixes some issues with the hex and quad cells.