Bug 31224: Add Koha::Biblio->metadata_record

Bug 31224: Add Koha::Biblio->metadata_record

This patch introduces a higher-level method for retrieving a 'prepared'
record for using in specific contexts. In particular, I only focused on
embedding item information and OPAC view filtering. But we could add a
way to get the record through the ViewPolicy also for staff.

The virtue of this patch is that it explains better than my words why I
think having the *embed_items* and *opac* parameters in
Koha::Biblio::Metadata->record is not ideal. And makes the other
implementation feel like is done at the wrong level.

I know it's been done like that to act as a drop-in replacement fro GetMarcBiblio,
which was a good first step. But we need to revisit how it is used, in general, to come
up with a more refined and useful design. So we do not port the same
design problems from C4::* into Koha::*.

Try to think how it would be used in contexts like opac-MARCdetail.pl or
any other OPAC controller script.

Thanks!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>