functionObjects::fieldValues::volFieldValue: Added support for VolInternalField

It is now possible to calculate field values of VolInternalFields, e.g. the
cached kEpsilon:G field in the
tutorials/modules/incompressibleFluid/pitzDailySteady case:

    #includeFunc cellMax(kEpsilon:G)

src/functionObjects/field/fieldValues/volFieldValue/volFieldValueTemplates.C

@@ -34,7 +34,11 @@ bool Foam::functionObjects::fieldValues::volFieldValue::validField
     const word& fieldName
 ) const
 {
-    if (obr_.foundObject<VolField<Type>>(fieldName))
+    if
+    (
+        obr_.foundObject<VolField<Type>>(fieldName)
+     || obr_.foundObject<VolInternalField<Type>>(fieldName)
+    )
     {
         return true;
     }
@@ -55,6 +59,14 @@ Foam::functionObjects::fieldValues::volFieldValue::getFieldValues
         return filterField(obr_.lookupObject<VolField<Type>>(fieldName));
     }
 
+    if (obr_.foundObject<VolInternalField<Type>>(fieldName))
+    {
+        return filterField
+        (
+            obr_.lookupObject<VolInternalField<Type>>(fieldName)
+        );
+    }
+
     FatalErrorInFunction
         << "Field " << fieldName << " not found in database"
         << abort(FatalError);

src/functionObjects/field/fieldsExpression/fieldsExpression.H

@@ -61,15 +61,6 @@ class fieldsExpression
 {
 protected:
 
-    // Protected typedefs
-
-        //- Internal field typedef that doesn't go via the
-        //  GeometricField::Internal typedef, and therefore allows template
-        //  argument deduction of the Type
-        template<class Type>
-        using VolInternalField = DimensionedField<Type, volMesh>;
-
-
     // Protected member data
 
         //- Names of fields to process