message: Add `GetNFaceNeighborElements` to `ParMesh`
diff: @@ -268,6 +268,7 @@ public:
  int ordering = 1);
  int GetNFaceNeighbors() const { return face_nbr_group.Size(); }
  + int GetNFaceNeighborElements() const { return face_nbr_elements.Size(); }
  int GetFaceNbrGroup(int fn) const { return face_nbr_group[fn]; }
  int GetFaceNbrRank(int fn) const;
  