Whole-row fixes for ALTER COLUMN SET EXPRESSION

Whole-row fixes for ALTER COLUMN SET EXPRESSION

When changing the expression of a generated column via ALTER TABLE
ALTER COLUMN SET EXPRESSION, objects that depend on the column via
indirect whole-row references (such as CHECK constraints, indexes)
must be handled specially, because technically pg_depend does not
contain such dependencies, see
recordDependencyOnSingleRelExpr->find_expr_references_walker.

This is a fix for commit f80bedd52, "Allow ALTER COLUMN SET EXPRESSION
on virtual columns with CHECK constraints".

Author: jian he <jian.universality@gmail.com>
Co-authored-by: Peter Eisentraut <peter@eisentraut.org>
Reported-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Reviewed-by: Ayush Tiwari <ayushtiwari.slg01@gmail.com>
Reviewed-by: solai v <solai.cdac@gmail.com>
Reviewed-by: Zsolt Parragi <zsolt.parragi@percona.com>
Discussion: https://www.postgresql.org/message-id/flat/CAJTYsWXOkyeDVbzymWc9sKrq7Y_MUv6XJXN4H9GfsBOPd3NJ+w@mail.gmail.com