ENH: add proximityRegions filter to distanceSurface (#2108)

• combines region-based and proximity-based filtering

  proxityRegions (post-filter): Checks the resulting faces against the original search surface as well as checking the cut cells for topological connectivity. If the area-weighted distance for a region is greater than \c absProximity, the region is discarded.

STYLE: support 'proxityFaces' as synonym for 'proximity' filter