Provide common face area/normal support in PrimitivePatch
For polyPatch, both the faceAreas() and faceCentres() are masked by their subField equivalents. Since there is no polyPatch method for magFaceAreas(), the PrimitivePatch method will be seen.
For polyPatch, both the faceAreas() and faceCentres() are masked by their subField equivalents. Since there is no polyPatch method for magFaceAreas(), the PrimitivePatch method will be seen.