GeometricField: Renamed internalField() -> primitiveField() and dimensionedInternalField() -> internalField()

These new names are more consistent and logical because:

primitiveField():
primitiveFieldRef():
    Provides low-level access to the Field<Type> (primitive field)
    without dimension or mesh-consistency checking.  This should only be
    used in the low-level functions where dimensional consistency is
    ensured by careful programming and computational efficiency is
    paramount.

internalField():
internalFieldRef():
    Provides access to the DimensionedField<Type, GeoMesh> of values on
    the internal mesh-type for which the GeometricField is defined and
    supports dimension and checking and mesh-consistency checking.

applications/solvers/DNS/dnsFoam/dnsFoam.C

@@ -61,7 +61,7 @@ int main(int argc, char *argv[])
     {
         Info<< "Time = " << runTime.timeName() << nl << endl;
 
-        force.internalFieldRef() = ReImSum
+        force.primitiveFieldRef() = ReImSum
         (
             fft::reverseTransform
             (