Retrieves the first day of the week for the given locale.
getLocaleFirstDayOfWeek(locale: string): WeekDay
A locale code for the locale format rules to use.
WeekDay: A day index number, using the 0-based week-day index for
en-US (Sunday = 0, Monday = 1, ...). For example, for
fr-FR, returns 1 to indicate that the first day is Monday.