- 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.