catalog/rewrite: handle UDF references from computed columns and ON UPDATE

When restoring a backup that has computed columns or ON UPDATE
expressions that reference UDFs, we need to check if the function
descriptor is available or needs to be rewritten. If it's not available,
the computed column expression or ON UPDATE expression is discarded. We
already had this behavior in place for DEFAULT exprssions, but did not
have this for other expressions when we added support for referencing
UDFs in de08f52 (v25.3.0).

Release note (bug fix): Fixed a bug that prevented RESTORE from working
if there were computed columns or ON UPDATE expressions that referenced
user-defined functions. This bug was introduced in v25.3.0.

Author: rafiss