Fixes #34366

Currently setting queue_name_prefix will not combine a prefix with the
default_queue_name; it will only affect queue names set with `queue_as`.
With this PR the prefix will affect the default_queue_name as well.

Closes #19831

Currently setting default_queue_name doesn't actually affect the
queue_name default (although default_queue_name does get used if you
pass a falsey `part_name` to `queue_as`). This PR would get
default_queue_name working as expected as well.

Because the queue_name default is now a lambda wrapping the
default_queue_name, rather than the default_queue_name itself, I had to
update one test to use the instance method `#queue_name` (which
`instance_exec`s the value) instead of the class method. I think this
change is OK, since only the instance method is documented.

There was a question about whether we want a `default_queue_name`
configuration. If we want to get rid of it, I would also be happy to
open a PR for that instead. It has been around for a while now, but it
also hasn't really worked for a while now.

r? @matthewd
since you had an opinion about this before