code: static void rollToNextWeekStart(DTBuilder builder, Weekday wkst) {
          DateValue bd = builder.toDate();
          builder.day += (7 - ((7 + (Weekday.valueOf(bd).javaDayNum
                  - wkst.javaDayNum))
                  % 7)) % 7;
          builder.normalize();
      }
docs: advances builder to the earliest day on or after builder that falls on
  wkst.
  @param builder non null.
  @param wkst the day of the week that the week starts on