Bug 9988: Add extract_biblionumber to Koha/SearchEngine

Bug 9988: Add extract_biblionumber to Koha/SearchEngine

When we will replace the Zebra code in sub merge, we will call SearchEngine
to pass records and we need a routine to extract a biblionumber from
a search result record. A record from Zebra still must be converted to
MARC::Record. This is no longer needed for a ElasticSearch record.

Test plan:
Run t/db_dependent/Koha/SearchEngine/Search.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jacek Ablewicz <abl@biblos.pk.edu.pl>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>