ENH: snappyHexMesh: work better on non-manifold. Fixes ##3361

Summary

• Handle inside/outside for incorrectly oriented surfaces
• adds 'smoothTriSurfaceMesh' version of triSurfaceMesh with interpolated normals

Resolved bugs (If applicable)

#3361 (closed)

Risks

• orients normals consistently so will behave differently from previous
• limited testing of smoothTriSurfaceMesh