Commit 7c15cef8 changed sql_identifier data type to be based on name
instead of varchar.  Unfortunately, this breaks on-disk format for this
data type.  Luckily, that should be a very rare problem, as this data
type is used only in information_schema views, so this only affects user
objects (tables, materialized views and indexes).  One way to end in
such situation is to do CTAS with a query on those system views.

There are two options to deal with this - we can either abort pg_upgrade
if there are user objects with sql_identifier columns in pg_upgrade, or
we could replace the sql_identifier type with varchar.  Considering how
rare the issue is expected to be, and the complexity of replacing the
data type (e.g. in matviews), we've decided to go with the simple check.

The query is somewhat complex - the sql_identifier data type may be used
indirectly - through a domain, a composite type or both, possibly in
multiple levels.  Detecting this requires a recursive CTE.

Backpatch to 12, where the sql_identifier definition changed.

Reported-by: Hans Buschmann
Author: Tomas Vondra
Reviewed-by: Tom Lane
Backpatch-to: 12
Discussion: https://postgr.es/m/16045-673e8fa6b5ace196%40postgresql.org