multicomponentThermo: Dimensioned constant specie properties

The specie molecular mass (Wi) and formation enthalpy (hfi) methods now
return dimensioned scalars. This permits their direct inclusion into
dimensioned field expressions. Non-dimensioned methods have been
retained with a "Value" suffix (i.e., WiValue and hfiValue).

applications/solvers/chemFoam/thermoTypeFunctions.H

@@ -32,7 +32,7 @@ scalarList W(const fluidMulticomponentThermo& thermo)
 
     forAll(W, i)
     {
-        W[i] = thermo.Wi(i);
+        W[i] = thermo.Wi(i).value();
     }
 
     return W;