Allow IS JSON predicate to work with domain types

Allow IS JSON predicate to work with domain types

The IS JSON predicate only accepted the base types text, json, jsonb, and
bytea.  Extend it to also accept domain types over those base types by
resolving through getBaseType() during parse analysis.

The base type OID is stored in the JsonIsPredicate node (as exprBaseType)
so the executor can dispatch to the correct validation path without
repeating the domain lookup at runtime.

When a non-supported type (or domain over a non-supported type) is used,
the error message displays the original type name as written by the user,
rather than the resolved base type.

Author: jian he <jian.universality@gmail.com>
Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Discussion: https://postgr.es/m/CACJufxEk34DnJFG72CRsPPT4tsJL9arobX0tNPsn7yH28J=zQg@mail.gmail.com