Error suppression support for upcoming jsonpath .datetime() method

Error suppression support for upcoming jsonpath .datetime() method

Add support of error suppression in some date and time manipulation functions
as it's required for jsonpath .datetime() method support.  This commit doesn't
use PG_TRY()/PG_CATCH() in order to implement that.  Instead, it provides
internal versions of date and time functions used, which support error
suppression.

Discussion: https://postgr.es/m/CAPpHfdsZgYEra_PeCLGNoXOWYx6iU-S3wF8aX0ObQUcZU%2B4XTw%40mail.gmail.com
Author: Alexander Korotkov, Nikita Glukhov
Reviewed-by: Anastasia Lubennikova, Peter Eisentraut