BUG #15616: extension functionality issues

The following bug has been logged on the website:

Bug reference: 15616
Logged by: Ivo Kohn
Email address: i(dot)kohn(at)seznam(dot)cz
PostgreSQL version: 11.0
Operating system: Ubuntu 16.04.5 LTS
Description:

Dear PostgreSQL developers,

we are using the extensions functionality
(https://www.postgresql.org/docs/11/extend-extensions.html) for the
developing and deploying SQL applications. During the usage of its features
we have encountered some problems which might be considered as bugs.

1) pg_dump with --schema parameter
The possibility of making "configuration tables" (e.g. SELECT
pg_catalog.pg_extension_config_dump('t_students', ''); ) within the
extension is a great option to mark tables as "user input tables". Maybe
it's not the way it supposed to be used but we appreciate it, the user has
to have the ability to dump its own data, not the data necessary for the
application to be run (e.g. lookups). Pg_dump then works fine, even with the
parameter --table. But the parameter --schema fails to dump data from
specified tables (marked with the pg_extension_config_dump) within the
schema.

2) Hanging OID in extconfig
Related issue. If the table (or sequence) was assigned to dump by
pg_extension_config_dump, its OID is still present in the field "extconfig"
of pg_extension after it was removed by DROP TABLE.

3) Extension owner
There is no easy way how to change it. We consider it as a bug because we
don't have on our minds any other object in the database whose owner cannot
be changed with the ALTER statement.

Thanks in advance for the consideration of fixing those issues.

Kind Regards,
Ivo Kohn.