ENH: improvements for GeometricBoundaryField evaluation
- early termination from evaluate_if() and evaluateCoupled().
- evaluateCoupled() now forwards to evaluate_if() and receives
additional handling for a 'void' parameter type.
BREAKING: extra template parameter for overset correctBoundaryCondition
- the true/false flag as a template parameter instead of as an
argument to use 'if constexpr' code