`time_zone_options_for_select` should show all time zones below the separator when priority time zones are specified.

Continuation of Pull Request #9620: [commit](https://github.com/lawrencepit/rails/commit/4ba40b23e49deb4c845ca16060939e5db921cfa1)

The following:

```
   f.time_zone_select :time_zone, [ ActiveSupport::TimeZone['Pacific Time (US & Canada)'] ]
```

will not show time zone "(GMT-08:00) Pacific Time (US & Canada)" below the separator, it will only show at the top of the options list.

We regularly get tickets from our users who say they get confused when they can't find the time zone (or country or language or etc.) in the (long) list below the options separator where they would expect to find the value. 

This usually happens when a user goes into edit mode and a non-priority option is selected (e.g. "(GMT-07:00) Arizona"), and they want to change it to a different selection. It's not obvious they then have to look at the top (as the top is often also out of sight). 

This patch always shows all time zone options below the separator, even when they are listed as a priority time zone.

See also [discussion](https://github.com/rails/rails/pull/9620#discussion-diff-3307962)