Returns a copy of this
LocalDateTime with the day-of-year altered.
If the resulting date-time is invalid, an exception is thrown.
This instance is immutable and unaffected by this method call.
|the day-of-year to set in the result, from 1 to 365-366|
LocalDateTime based on this date with the requested day, not null
|if the day-of-year value is invalid, or if the day-of-year is invalid for the year|