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

src/parallel/reconstruct/faReconstruct/faMeshReconstructor.C

@@ -495,7 +495,7 @@ void Foam::faMeshReconstructor::createMesh()
     auto& completeMesh = *serialAreaMesh_;
 
     // Add in non-processor boundary patches
-    PtrList<faPatch> completePatches(singlePatchEdgeLabels_.size());
+    faPatchList completePatches(singlePatchEdgeLabels_.size());
     forAll(completePatches, patchi)
     {
         const labelList& patchEdgeLabels = singlePatchEdgeLabels_[patchi];