enableDay method
当前日期是否可用
Implementation
bool enableDay(DateDay day, DateMonth month) =>
day.inMonth(month) &&
((_minDay != null && _minDay! <= day) || _minDay == null) &&
((_maxDay != null && _maxDay! >= day) || _maxDay == null) &&
(_enableDays == null || _enableDays!.contains(day));