Bug 30576: (follow-up) Corrections to behaviour to reflect unit tests

Bug 30576: (follow-up) Corrections to behaviour to reflect unit tests

The unit tests highlighted my original patch didn't cover the full
preference description.

We now replace the 'standard' option with the fields from the preference
and we also add those fields as options to the field selection in
advanced searches.

This patch also adjusts the tests to test for that and reflects the
expected changes to the number of options displayed in the select boxes.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>