ENH: update CompactListList code

- eliminate redundant size_ accounting

- drop extra 'Container' template parameter and replace functionality
  with more flexible pack/unpack methods.
  There is also a pack() method that handles indirect lists of lists
  that can be used, for example, to pack a patch slice of faces.

  Drop the 'operator()' method in favour of unpack to expose and properly
  document the conversion. Should revisit the corresponding code in
  some places for optimization potential.

- align some method names with globalIndex:
  totalSize(), maxSize() etc

src/parallel/decompose/decompositionMethods/multiLevelDecomp/multiLevelDecomp.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2021 OpenCFD Ltd.
+    Copyright (C) 2017-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -614,7 +614,7 @@ Foam::labelList Foam::multiLevelDecomp::decompose
 
     decompose
     (
-        cellCells(),
+        cellCells.unpack(),
         cc,
         cWeights,
         cellMap,      // map back to original cells