ENH: added IndirectSubList

- provides an indirect access to a sub-section of a list that is
  somewhat less efficient than a Foam::SubList, but supports the
  following:
    * adjustment of its addressing range after construction
    * recovery of the original, underlying list at any time

  This can be more convenient for some coding cases.
  For example,

      template<class Addr>
      void renumberFaces(IndirectListBase<face, Addr>& faces, ...);

  which can be called for

      * Specific faces:
        UIndirectList<face>(mesh.faces(), facesToChange)

      * A sub-range of faces:
        IndirectSubList<face>(mesh.faces(), pp.range())

      * All faces:
        IndirectSubList<face>(mesh.faces())

CONFIG: added IndirectListsFwd.H with some common forwarding

applications/test/sliceRange/Test-sliceRange.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -31,8 +31,9 @@ Description
 #include "labelList.H"
 #include "FixedList.H"
 #include "sliceRange.H"
-#include "SliceList.H"
 #include "IndirectList.H"
+#include "IndirectSubList.H"
+#include "SliceList.H"
 #include "Random.H"
 
 using namespace Foam;
@@ -146,6 +147,23 @@ int main(int argc, char *argv[])
 
         Info<< nl << "Random list: " << flatOutput(list1) << nl;
 
+        {
+            IndirectSubList<scalar> sublist1(list1, labelRange(0, 10));
+
+            Info<< nl << "SubList: " << sublist1.addressing() << " = "
+                << flatOutput(sublist1) << nl;
+
+            // Adjust addressing
+            sublist1.addressing().reset(5, 8);
+
+            // This should resolve as a no-op
+            sublist1 = sublist1;
+
+            Info<< "SubList: " << sublist1.addressing() << " = "
+                << flatOutput(sublist1) << nl;
+        }
+
+
         SliceList<scalar> slice1(list1, sliceRange(0, 15, 3));
 
         Info<< nl << "slicing with: " << slice1.addressing() << nl;