BUG #16250: As the owner of a database, I can't CREATE EXTENSION postgis;

The following bug has been logged on the website:

Bug reference: 16250
Logged by: Randy Strauss
Email address: randolph.a.strauss@nasa.gov
PostgreSQL version: 10.5
Operating system: Mac
Description:

The documentation looks identical for 10.5 and 12 with respect to
extensions.

There's no point being able to create a database if one can't add the
extensions one needs.
We need postgis, postgis_topology, uuid-ossp, hstore
How about adding a privilege to control this, instead of forcing the
superuser password to be given out?

I don't know if this is a bug. I don't see it on the FAQ or TODO list...
I don't see a "requires superuser" field in the pg_extension table...