ENH: improved handling for clamping

- proper component-wise clamping for MinMax clamp().

- construct clampOp from components

- propagate clamp() method from GeometricField to FieldField and Field

- clamp_min() and clamp_max() for one-sided clamping,
  as explicit alternative to min/max free functions which can
  be less intuitive and often involve additional field copies.

- top-level checks to skip applying invalid min/max ranges
  and bypass the internal checks of MinMax::clamp() etc.

applications/utilities/preProcessing/PDR/pdrFields/PDRarraysCalc.C

@@ -1279,7 +1279,7 @@ void write_scalarField
             continue;
         }
 
-        os << limits.clip(fld(cellIdx)) << nl;
+        os << limits.clamp(fld(cellIdx)) << nl;
     }
 
     os << token::END_LIST << token::END_STATEMENT << nl;