add a setOption(int num) hook to ChoiceInstance
If host does not support kOfxParamPropChoiceLabelOption, use  kOfxParamPropHint instead

see
https://github.com/tuttleofx/TuttleOFX/commit/ae6e14e99f62b5efa89e4de4a3
bc33129ac6afd0
(same patch was applied both in ChoiceParam::appendOption() and
ChoiceParamDescriptor::appendOption())