stitchMesh: Replacement utility based on the new patchIntersection algorithm

The mergePatchPairs functionality in blockMesh also now uses patchIntersection.

The new mergePatchPairs and patchIntersection replaces the old, fragile and
practically unusable polyTopoChanger::slidingInterface functionality the removal
of which has allowed the deletion of a lot of other ancient and otherwise unused
clutter including polyTopoChanger, polyMeshModifier, polyTopoChange::setAction
and associated addObject/*, modifyObject/* and removeObject/*.  This
rationalisation paves the way for the completion of the update of zone handling
allowing mesh points, faces and cells to exist in multiple zones which is
currently not supported with mesh topology change.

Application
    stitchMesh

Description
    Utility to stitch or conform pairs of patches,
    converting the patch faces either into internal faces
    or conformal faces or another patch.

Usage
    \b stitchMesh (\<list of patch pairs\>)

    E.g. to stitch patches \c top1 to \c top2 and \c bottom1 to \c bottom2
        stitchMesh "((top1 top2) (bottom1 bottom2))"

    Options:
      - \par -overwrite \n
        Replace the old mesh with the new one, rather than writing the new one
        into a separate time directory

      - \par -region \<name\>
        Specify an alternative mesh region.

      - \par -fields
        Update vol and point fields

      - \par -tol
        Merge tolerance relative to local edge length (default 1e-4)

See also
    Foam::mergePatchPairs

Author: Henry Weller

applications/utilities/mesh/generation/blockMesh/blockMesh.C

@@ -2,7 +2,7 @@
   =========                 |
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     | Website:  https://openfoam.org
-    \\  /    A nd           | Copyright (C) 2011-2021 OpenFOAM Foundation
+    \\  /    A nd           | Copyright (C) 2011-2023 OpenFOAM Foundation
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
 License
@@ -48,24 +48,16 @@ Usage
 
 \*---------------------------------------------------------------------------*/
 
+#include "argList.H"
 #include "Time.H"
-#include "IOdictionary.H"
-#include "IOPtrList.H"
 #include "systemDict.H"
-
 #include "blockMesh.H"
-#include "attachPolyTopoChanger.H"
+#include "mergePatchPairs.H"
 #include "polyTopoChange.H"
 #include "emptyPolyPatch.H"
 #include "cyclicPolyPatch.H"
-
-#include "argList.H"
-#include "OSspecific.H"
 #include "OFstream.H"
 
-#include "Pair.H"
-#include "slidingInterface.H"
-
 using namespace Foam;
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
@@ -236,22 +228,23 @@ int main(int argc, char *argv[])
     // Read in a list of dictionaries for the merge patch pairs
     if (meshDict.found("mergePatchPairs"))
     {
-        List<Pair<word>> mergePatchPairs
+        List<Pair<word>> patchPairNames
         (
             meshDict.lookup("mergePatchPairs")
         );
 
-        #include "mergePatchPairs.H"
+        if (patchPairNames.size())
+        {
+            const word oldInstance = mesh.pointsInstance();
+            mergePatchPairs(mesh, patchPairNames, 1e-4);
+            mesh.setInstance(oldInstance);
+        }
     }
     else
     {
-        Info<< nl << "There are no merge patch pairs edges" << endl;
+        Info<< nl << "No patch pairs to merge" << endl;
     }
 
-
-    // Set any cellZones (note: cell labelling unaffected by above
-    // mergePatchPairs)
-
     label nZones = blocks.numZonedBlocks();
 
     if (nZones > 0)