Extend DomainHasConstraints() to optionally check constraint volatility

Extend DomainHasConstraints() to optionally check constraint volatility

Add an optional bool *has_volatile output parameter to
DomainHasConstraints().  When non-NULL, the function checks whether any
CHECK constraint contains a volatile expression.  Callers that don't
need this information pass NULL and get the same behavior as before.

This is needed by a subsequent commit that enables the fast default
optimization for domains with non-volatile constraints: we can safely
evaluate such constraints once at ALTER TABLE time, but volatile
constraints require a full table rewrite.

Author: Jian He <jian.universality@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Reviewed-by: Viktor Holmberg <viktor.holmberg@aiven.io>
Discussion: https://postgr.es/m/CACJufxE_+iZBR1i49k_AHigppPwLTJi6km8NOsC7FWvKdEmmXg@mail.gmail.com