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