ENH: support creation of boundaries/zones from list of entries

- this makes it easier to split creation into a two-stage process
  as required

- extend handling for polyBoundaryMeshEntries, faBoundaryMeshEntries
  with more functionality. Ensure that these are never registered.

ENH: addition writeEntry methods for polyBoundaryMesh

- simplifies streaming and collating into other files

ENH: polyMesh rereading - update owner/neighbour header information

- this avoids accidentally reading the "cells" file if the mesh has
  been created with NO_READ and then updated

STYLE: less vertical space when outputting empty PtrList

applications/test/boundaryMeshEntries/Make/files

@@ -0,0 +1,3 @@
+Test-boundaryMeshEntries.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-boundaryMeshEntries

applications/test/boundaryMeshEntries/Make/options

@@ -0,0 +1,2 @@
+/* EXE_INC = */
+/* EXE_LIBS = */

applications/test/boundaryMeshEntries/Test-boundaryMeshEntries.C

@@ -0,0 +1,146 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-boundaryMeshEntries
+
+Description
+    Find and print "boundary" information
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+
+#include "fileName.H"
+#include "IOstreams.H"
+#include "polyMesh.H"
+#include "polyBoundaryMeshEntries.H"
+#include "OSspecific.H"
+#include "Time.H"
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// Main program:
+
+int main(int argc, char *argv[])
+{
+    argList::noFunctionObjects();  // Disallow function objects
+    argList::addVerboseOption("additional verbosity");
+
+    #include "setRootCase.H"
+    #include "createTime.H"
+
+    fileName coherentInst;
+    coherentInst =
+    (
+        runTime.findInstance
+        (
+            polyMesh::meshSubDir,
+            "coherent",
+            IOobject::READ_IF_PRESENT
+        )
+    );
+
+    // Unfortunately with READ_IF_PRESENT, cannot tell if the file
+    // was actually found or not
+
+    Info<< "check: " << (coherentInst/polyMesh::meshSubDir/"coherent") << nl;
+
+    if (!Foam::isFile(coherentInst/polyMesh::meshSubDir/"coherent"))
+    {
+        coherentInst.clear();
+    }
+
+    Info<< "found coherent: " << coherentInst << nl;
+
+    PtrList<entry> entries;
+
+    if (!coherentInst.empty())
+    {
+        IOdictionary coherent
+        (
+            IOobject
+            (
+                "coherent",
+                coherentInst,
+                polyMesh::meshSubDir,
+                runTime,
+                IOobject::MUST_READ,
+                IOobject::NO_WRITE,
+                IOobject::NO_REGISTER
+            )
+        );
+
+        ITstream& is = coherent.lookup("boundary");
+        is >> entries;
+    }
+
+    Info<< "entries: " << entries << nl;
+
+    Info<< "type:  " << polyBoundaryMeshEntries::types(entries) << nl;
+    Info<< "start: " << polyBoundaryMeshEntries::patchStarts(entries) << nl;
+    Info<< "size: "  << polyBoundaryMeshEntries::patchSizes(entries) << nl;
+    Info<< nl;
+
+    fileName boundaryInst;
+    boundaryInst =
+    (
+        runTime.findInstance
+        (
+            polyMesh::meshSubDir,
+            "boundary",
+            IOobject::MUST_READ
+        )
+    );
+
+    Info<< "found boundary: " << boundaryInst << nl;
+
+    polyBoundaryMeshEntries pbm
+    (
+        IOobject
+        (
+            "boundary",
+            boundaryInst,
+            polyMesh::meshSubDir,
+            runTime,
+            IOobject::MUST_READ,
+            IOobject::NO_WRITE,
+            IOobject::NO_REGISTER
+        )
+    );
+
+    Info<< "type:  " << flatOutput(pbm.types()) << nl;
+    Info<< "start: " << flatOutput(pbm.patchStarts()) << nl;
+    Info<< "size: "  << flatOutput(pbm.patchSizes()) << nl;
+
+    pbm.writeEntry("boundary", Info);
+
+    Info<< "\nEnd\n" << endl;
+    return 0;
+}
+
+
+// ************************************************************************* //