ENH: add read/write specialization for lists of character data

- read/write lists of character data in binary only.
  This is the only means of preserving data.
  If character data are written as an ASCII list, there is no means of
  determining if spaces or newlines are content or separators.

applications/test/charList/Make/files

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

applications/test/charList/Make/options

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

applications/test/charList/Test-charList.C

@@ -0,0 +1,87 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2021 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-charList
+
+Description
+    Some test of UList, List for characters
+
+\*---------------------------------------------------------------------------*/
+
+#include "OSspecific.H"
+#include "argList.H"
+#include "IOstreams.H"
+#include "messageStream.H"
+
+#include "charList.H"
+#include "labelList.H"
+#include "StringStream.H"
+#include "ListOps.H"
+#include "SubList.H"
+#include "FlatOutput.H"
+
+#include <numeric>
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+//  Main program:
+
+int main(int argc, char *argv[])
+{
+    argList::noBanner();
+    argList::noParallel();
+    argList::noFunctionObjects();
+
+    #include "setRootCase.H"
+
+    Info<< "Known compound tokens: "
+        << token::compound::IstreamConstructorTablePtr_->sortedToc() << nl;
+
+    OStringStream ostr;
+
+    {
+        List<char> alphabet(64);
+        std::iota(alphabet.begin(), alphabet.end(), '@');
+
+        alphabet.writeEntry("alphabet", Info);
+
+        ostr << alphabet;
+
+        Info<< "wrote: " << ostr.str() << nl;
+    }
+
+    {
+        IStringStream istr(ostr.str());
+        List<char> alphabet(istr);
+
+        Info<< "re-read: " << alphabet << nl;
+    }
+
+    return 0;
+}
+
+// ************************************************************************* //