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/utilities/parallelProcessing/decomposePar/pointFieldDecomposerDecomposeFields.C

@@ -36,7 +36,7 @@ Foam::pointFieldDecomposer::decomposeField
 ) const
 {
     // Create and map the internal field values
-    Field<Type> internalField(field.internalField(), pointAddressing_);
+    Field<Type> internalField(field.primitiveField(), pointAddressing_);
 
     // Create a list of pointers for the patchFields
     PtrList<pointPatchField<Type>> patchFields(boundaryAddressing_.size());