ENH: improve processor topology handling in zoneDistribute (#2371)

- now largely encapsulated using PstreamBuffers methods,
  which makes it simpler to centralize and maintain

- avoid building intermediate structures when sending data,
  remove unused methods/data

TUT: parallel version of depthCharge2D

STYLE: minor update in ProcessorTopology

tutorials/multiphase/compressibleInterIsoFoam/laminar/depthCharge2D/Allrun-parallel

@@ -0,0 +1,18 @@
+#!/bin/sh
+cd "${0%/*}" || exit                                # Run from this directory
+. ${WM_PROJECT_DIR:?}/bin/tools/RunFunctions        # Tutorial run functions
+#------------------------------------------------------------------------------
+
+runApplication blockMesh
+
+restore0Dir
+
+runApplication setFields
+
+runApplication setAlphaField
+
+decomposePar
+
+runParallel $(getApplication)
+
+#------------------------------------------------------------------------------

tutorials/multiphase/compressibleInterIsoFoam/laminar/depthCharge2D/system/decomposeParDict

@@ -0,0 +1,27 @@
+/*--------------------------------*- C++ -*----------------------------------*\
+| =========                 |                                                 |
+| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
+|  \\    /   O peration     | Version:  v2112                                 |
+|   \\  /    A nd           | Website:  www.openfoam.com                      |
+|    \\/     M anipulation  |                                                 |
+\*---------------------------------------------------------------------------*/
+FoamFile
+{
+    version     2.0;
+    format      ascii;
+    class       dictionary;
+    object      decomposeParDict;
+}
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+numberOfSubdomains 8;
+
+method          hierarchical;
+
+coeffs
+{
+    n           (4 2 1);
+}
+
+
+// ************************************************************************* //