ENH: shm: support for automatic faceZones

Summary

Extends meshing of faceZones to allow having multiple faceZones per surface

Details of new models (If applicable)

Currently a single (explicitly named) faceZone can be specified for a surface. This new functionality extends it to have a separate faceZone for every region of the surface.

Risks

The default behaviour has not changed. A new keyword, faceZoneNaming, can switch on the new behaviour. See the new mesh/snappyHexMesh/faceZoneRegions tutorial