firstSundayFromWeekInYear function
Gets the date of the sunday of a week in a year.
Implementation
DateTime firstSundayFromWeekInYear(int weekNumber, int year) {
final DateTime weekDay = DateTime(2022).add(Duration(days: (weekNumber - 2) * 7));
return weekDay.add(Duration(days: (DateTime.sunday - weekDay.weekday) % DateTime.daysPerWeek));
}