ENH: consolidate processorTopology handling for volume and area meshes

- relocate templating to factory method 'New'.
  Adds provisions for more general re-use.

- expose processor topology in globalMesh as topology()

- wrap proc->patch lookup as processorTopology::procPatchLookup method
  (failsafe). May consider using Map<label> for its storage in the
  future.

src/sampling/meshToMesh/meshToMesh.C

@@ -31,6 +31,7 @@ License
 #include "globalIndex.H"
 #include "meshToMeshMethod.H"
 #include "nearestFaceAMI.H"
+#include "processorPolyPatch.H"
 #include "faceAreaWeightAMI.H"
 
 // * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //