The convenience accessors getYear getMonth and getDay in
TimestampWithTimeZone return long even though their values fall within
the range of int. This makes them a bit inconvenient to work with as
most APIs (Calendar, LocalDateTime) take int for such values.

This commit contains the following changes

 - change TimestampWithTimeZone#getYear() to return an int instead of
   a long
 - change TimestampWithTimeZone#getMonth() to return an int instead of
   a long
 - change TimestampWithTimeZone#getDay() to return an int instead of
   a long