[PG19] pg_upgrade --check passes, then the upgrade fails

i hackers,

From 18 to 19, pg_upgrade --check passes for both of these, then the
upgrade fails:

alter role app set standard_conforming_strings = off;
ERROR: non-standard string literals are not supported

create cast (uuid as bytea) with function uuid_send(uuid);
ERROR: cast from type uuid to type bytea already exists

With the patches, --check reports these before the upgrade starts.
0001 lists roles, databases and functions that store a setting the new
cluster rejects.

0002 lists user casts that are now built in. Both ask the new cluster,
so the next removed setting or new cast is caught too.

Both work like check_loadable_libraries(), which collects names from the
old cluster and tries them on the new one.

0003 is a optional test

I think this is a 19 open item.

Thanks,
Shihao