Closes bpo-28292: Implemented Calendar.itermonthdays3() and itermonthdays4(). (#4079)

Calendar.itermonthdates() will now consistently raise an exception when a date falls outside of the 0001-01-01 through 9999-12-31 range. To support applications that cannot tolerate such exceptions, the new methods itermonthdays3() and itermonthdays4() are added. The new methods return tuples and are not restricted by the range supported by datetime.date.

Thanks @serhiy-storchaka for suggesting the itermonthdays4() method and for the review.