BUG #19878: pg_identify_object functions expose XX000 for unsupported class IDs

The following bug has been logged on the website:

Bug reference: 19878
Logged by: Faye
Email address: imchifan(at)mail(dot)com
PostgreSQL version: 18.6
Operating system: Linux/amd64
Description:

Passing an unsupported class ID to pg_identify_object() or
pg_identify_object_as_address() produces SQLSTATE XX000 (internal_error).
These public object-address inspection functions should classify invalid
user input as SQLSTATE 22023 (invalid_parameter_value) instead.

The block below records pg_describe_object() as a comparison, but its result
is not part of the assertion. The assertion applies only to the two
pg_identify_* functions.

How to repeat:

Save this as reproducer.sql and run `psql -X -d postgres -f reproducer.sql`:

```
-- The two pg_identify_* functions take the same (classid, objid, objsubid)
-- address as pg_describe_object() and must classify an unsupported classid
as
-- invalid_parameter_value (22023), never internal_error (XX000).
-- describe_code is recorded only as a comparison and is not asserted.
DO $object_address$
DECLARE
describe_code text;
identify_code text;
address_code text;
BEGIN
BEGIN
PERFORM pg_describe_object(1::oid, 1::oid, 0);
EXCEPTION WHEN OTHERS THEN
GET STACKED DIAGNOSTICS describe_code = RETURNED_SQLSTATE;
END;

BEGIN
PERFORM pg_identify_object(1::oid, 1::oid, 0);
EXCEPTION WHEN OTHERS THEN
GET STACKED DIAGNOSTICS identify_code = RETURNED_SQLSTATE;
END;

BEGIN
PERFORM pg_identify_object_as_address(1::oid, 1::oid, 0);
EXCEPTION WHEN OTHERS THEN
GET STACKED DIAGNOSTICS address_code = RETURNED_SQLSTATE;
END;

RAISE NOTICE 'describe=%, identify=%, as_address=%',
describe_code, identify_code, address_code;

IF identify_code IS DISTINCT FROM '22023'
OR address_code IS DISTINCT FROM '22023' THEN
RAISE EXCEPTION
'oracle failed: describe=%, identify=%, as_address=% (expected
22023)',
describe_code, identify_code, address_code;
END IF;
END
$object_address$;

-- DO creates no persistent database objects; cleanup is vacuous.
```

I get the following output:

```
NOTICE: describe=XX000, identify=XX000, as_address=XX000
ERROR: oracle failed: describe=XX000, identify=XX000, as_address=XX000
(expected 22023)
CONTEXT: PL/pgSQL function inline_code_block line 30 at RAISE
```

The issue was reproduced on PostgreSQL 18.6 on Linux/amd64. The anonymous
block creates no persistent database objects, and the server remains usable
after the error.

This occurs when object-address inspection code passes an unsupported class
ID to pg_identify_object() or pg_identify_object_as_address().