ENH: extend type aliases to include geometric boundary fields (#2348)

STYLE: LduInterfaceFieldPtrsList as alias instead of a class

STYLE: define patch lists typedefs when defining the base patch

- eg, polyPatchList typedef within polyPatch.H

INT: relocate GeometricField::Boundary -> GeometricBoundaryField

- was internal to GeometricField but moving it outside simplifies
  forward declarations etc. Code adapted from openfoam.org

applications/utilities/parallelProcessing/decomposePar/domainDecomposition.C

@@ -419,7 +419,7 @@ bool Foam::domainDecomposition::writeDecomposition(const bool decomposeSets)
             nInterProcPatches += curSubPatchIDs[procPatchi].size();
         }
 
-        PtrList<polyPatch> procPatches
+        polyPatchList procPatches
         (
             curPatchSizes.size() + nInterProcPatches
         );