ENH: extend GeoMesh interface to include boundary_size() static method

- can be used to pre-allocate space for internal+boundary field for
  flat addressing (issue #3364).

  For example:

      DynamicField<Type> fld
      (
          std::pair<label,label>
          (
              GeoMesh::size(mesh),
              GeoMesh::size(mesh)
            + (extra ? GeoMesh::boundary_size(mesh) : label(0))
          )
      );

ENH: base changes for GeometricField flags

- FieldBase 'localBoundaryConsistency_' and 'localBoundaryTolerance_'
  for central handling of local boundary consistency checks.

- FieldBase 'unifiedGeometricField' for future extensions to GeometricField