_buildDayNames(localeData) {
      if (this._hidden) {
        return; // Optimization to not do any work unless the current picker
      }

      let dayOfTheWeek;
      const aDayNamesWide = localeData.getDays("wide", this._primaryCalendarType);
      const aDayNamesAbbreviated = localeData.getDays("abbreviated", this._primaryCalendarType);
      let dayName;
      this._dayNames = [];
      this._dayNames.push({
        classes: "ui5-dp-dayname",
        name: DayPicker_1.i18nBundle.getText(_i18nDefaults.DAY_PICKER_WEEK_NUMBER_TEXT)
      });
      for (let i = 0; i < DAYS_IN_WEEK; i++) {
        dayOfTheWeek = i + this._getFirstDayOfWeek();
        if (dayOfTheWeek > DAYS_IN_WEEK - 1) {
          // 0-indexed so index of 6 is the maximum allowed
          dayOfTheWeek -= DAYS_IN_WEEK;
        }
        dayName = {
          name: aDayNamesWide[dayOfTheWeek],
          ultraShortName: aDayNamesAbbreviated[dayOfTheWeek],
          classes: "ui5-dp-dayname"
        };
        this._dayNames.push(dayName);
      }
      this._dayNames[1].classes += " ui5-dp-firstday";
      if (this.shouldHideWeekNumbers) {
        this._dayNames.shift();
      }
    }
Builds the dayNames object (header of the month).
@param { LocaleData } localeData
@private