ENH: add filtering version of dictionary copy

- can be useful when extracting portions of larger field files

applications/test/dictionaryCopy/Make/files

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+Test-dictionaryCopy.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-dictionaryCopy

applications/test/dictionaryCopy/Make/options

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+EXE_INC =

applications/test/dictionaryCopy/Test-dictionaryCopy.C

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+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  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, distributed under GPL-3.0-or-later.
+
+Application
+    Test-dictionaryCopy
+
+Description
+    Test copying a dictionary with filtering
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "IOobject.H"
+#include "IOstreams.H"
+#include "IFstream.H"
+#include "dictionaryContent.H"
+
+using namespace Foam;
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+//  Main program:
+
+int main(int argc, char *argv[])
+{
+    argList::noParallel();
+    argList::addArgument("dict .. dictN");
+    argList args(argc, argv, false, true);
+
+    const wordRes allow;
+    const wordRes deny
+    ({
+        wordRe("boundary.*", wordRe::REGEX)
+    });
+
+    Info<< nl
+        << "allow: " << flatOutput(allow) << nl
+        << "deny:  " << flatOutput(deny) << nl << nl;
+
+    if (args.size() <= 1)
+    {
+        const string dictFile = "testDictCopy";
+        IFstream is(dictFile);
+
+        dictionary input(is);
+
+        dictionary copied
+        (
+            dictionaryContent::copyDict
+            (
+                input,
+                allow,
+                deny
+            )
+        );
+
+        IOobject::writeDivider(Info);
+        input.writeEntry("input", Info);
+        copied.writeEntry("copied", Info);
+    }
+
+    for (label argi=1; argi < args.size(); ++argi)
+    {
+        const string& dictFile = args[argi];
+        IFstream is(dictFile);
+
+        dictionary input(is);
+
+        dictionary copied
+        (
+            dictionaryContent::copyDict
+            (
+                input,
+                allow,
+                deny
+            )
+        );
+
+        IOobject::writeDivider(Info);
+        input.writeEntry("input", Info);
+        copied.writeEntry("copied", Info);
+    }
+
+    IOobject::writeEndDivider(Info);
+
+    return 0;
+}
+
+
+// ************************************************************************* //

applications/test/dictionaryCopy/testDictCopy

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+/*--------------------------------*- C++ -*----------------------------------*\
+| =========                 |                                                 |
+| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
+|  \\    /   O peration     | Version:  v2012                                 |
+|   \\  /    A nd           | Website:  www.openfoam.com                      |
+|    \\/     M anipulation  |                                                 |
+\*---------------------------------------------------------------------------*/
+FoamFile
+{
+    version     2.0;
+    format      ascii;
+    class       dictionary;
+    object      testDictCopy;
+}
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+dimensions     [ 1 2 -2 0 0 0 0 ];
+
+internalField   uniform 1;
+
+boundaryField
+{
+    inlet_1  { type patch; }
+    inlet_2  { type patch; }
+}
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //