ENH: Added new multiRegion function object

Wrapper that clones the supplied object for each region.

Simplifies the setup of identical post-processing requirements for
multi-region cases.
Applies the supplied function to all regions by default.

Example of function object specification:

    multiRegion
    {
        type    multiRegion;
        libs    (utilityFunctionObjects);
        ...

        function
        {
            // Actual object specification
            type    fieldMinMax;
            libs    (fieldFunctionObjects);
            fields  (<field1> .. <fieldN>);
        }

        // Optional entries
        regions     (region1 region2);
    }

    Where the entries comprise:
        Property   | Description                    | Reqd | Default
        type       | Type name: multiRegion         | yes |
        function   | Function object sub-dictionary | yes |
        regions    | List of region names           | no  | all

src/functionObjects/utilities/multiRegion/multiRegion.H

@@ -0,0 +1,158 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  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/>.
+
+Class
+    Foam::functionObjects::multiRegion
+
+Group
+    grpUtilitiesFunctionObjects
+
+Description
+    Wrapper that clones the supplied function object for each region.
+
+    Simplifies the setup of identical post-processing requirements for
+    multi-region cases.
+    Applies the supplied function to all regions by default.
+
+Usage
+    Minimal example by using \c system/controlDict.functions:
+    \verbatim
+    multiRegion
+    {
+        // Mandatory entries
+        type    multiRegion;
+        libs    (utilityFunctionObjects);
+
+        function
+        {
+            // Actual object specification
+            type    fieldMinMax;
+            libs    (fieldFunctionObjects);
+            fields  (<field1> ... <fieldN>);
+        }
+
+        // Optional entries
+        regions     (region1 region2);
+    }
+    \endverbatim
+
+    where the entries mean:
+    \table
+      Property   | Description                          | Type | Reqd | Deflt
+      type       | Type name: multiRegion               | word | yes  | -
+      libs       | Library name: utilityFunctionObjects | word | yes  | -
+      function   | Function object sub-dictionary       | dict | yes  | -
+      regions    | List of region names                 | wordList | no  | all
+    \endtable
+
+See also
+  - Foam::functionObject
+
+SourceFiles
+    multiRegion.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef functionObjects_multiRegion_H
+#define functionObjects_multiRegion_H
+
+#include "timeFunctionObject.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+
+/*---------------------------------------------------------------------------*\
+                        Class multiRegion Declaration
+\*---------------------------------------------------------------------------*/
+
+class multiRegion
+:
+    public functionObjects::timeFunctionObject
+{
+protected:
+
+    // Protected Data
+
+        //- List of cloned objects (1 per region)
+        PtrList<functionObject> functions_;
+
+
+    // Protected Member Functions
+
+        //- No copy construct
+        multiRegion(const multiRegion&) = delete;
+
+        //- No copy assignment
+        void operator=(const multiRegion&) = delete;
+
+
+public:
+
+    //- Runtime type information
+    TypeName("multiRegion");
+
+
+    // Constructors
+
+        //- Construct from Time and dictionary
+        multiRegion
+        (
+            const word& name,
+            const Time& runTime,
+            const dictionary& dict
+        );
+
+
+    //- Destructor
+    virtual ~multiRegion() = default;
+
+
+    // Member Functions
+
+        //- Read the controls
+        virtual bool read(const dictionary& dict);
+
+        //- Execute, currently does nothing
+        virtual bool execute();
+
+        //- Write the multiRegion
+        virtual bool write();
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace functionObjects
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //