ENH: simplify calling of decomposition, support CompactListList

- combined most of the unweighted and weighted decomposition routines
  such that an empty weight field is treated as uniform weighting.
  This allows default parameters and cuts down on the number of
  decompose methods.

- for topology-driven decomposition, it is now possible to pass in the
  owner/neighbour connectivity as a CompactListList directly instead
  of first creating a labelListList (which was internally repacked into
  a CompactListList in many cases).
  However, multiLevelDecomp still uses unpacking (to avoid a larger
  reworking of code).

- support direct creation of some methods (eg, random, scotch etc)
  without a dictionary

- fix incorrect neighbour face weighting (fixes #3019)

ENH: relocate calcCellCells from decompositionMethod to globalMeshData

- makes it more universally available

src/parallel/decompose/decompositionMethods/structuredDecomp/structuredDecomp.H

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2012 OpenFOAM Foundation
-    Copyright (C) 2018-2021 OpenCFD Ltd.
+    Copyright (C) 2018-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef structuredDecomp_H
-#define structuredDecomp_H
+#ifndef Foam_structuredDecomp_H
+#define Foam_structuredDecomp_H
 
 #include "decompositionMethod.H"
 #include "wordRes.H"
@@ -61,7 +61,9 @@ class structuredDecomp
         autoPtr<decompositionMethod> method_;
 
 
-    // Private Member Functions
+public:
+
+    // Generated Methods
 
         //- No copy construct
         structuredDecomp(const structuredDecomp&) = delete;
@@ -70,8 +72,6 @@ class structuredDecomp
         void operator=(const structuredDecomp&) = delete;
 
 
-public:
-
     //- Runtime type information
     TypeName("structured");
 
@@ -102,16 +102,29 @@ public:
         (
             const polyMesh& mesh,
             const pointField& points,
-            const scalarField& pointWeights
+            const scalarField& pointWeights = scalarField::null()
         ) const;
 
+        //- Return for every coordinate the wanted processor number.
+        //  Explicitly provided connectivity - does not use mesh_.
+        virtual labelList decompose
+        (
+            const CompactListList<label>& globalCellCells,
+            const pointField& cc,
+            const scalarField& cWeights = scalarField::null()
+        ) const
+        {
+            NotImplemented;
+            return labelList();
+        }
+
         //- Return for every coordinate the wanted processor number.
         //  Explicitly provided connectivity - does not use mesh_.
         virtual labelList decompose
         (
             const labelListList& globalCellCells,
             const pointField& cc,
-            const scalarField& cWeights
+            const scalarField& cWeights = scalarField::null()
         ) const
         {
             NotImplemented;