LP#1609556: only include OPAC-visible copies in SRU/Z39.50 holdings

LP#1609556: only include OPAC-visible copies in SRU/Z39.50 holdings

To test:

1. Create a bib record.
2. Add an item to the record at BR1. Mark it as not OPAC-visible.
3. Do a CONS-level SRU search for the record, including holdings. The
   record is not included in results because there are no OPAC-visible
   holdings.
4. Add a second item to the same record, this time at BR3. Mark this
   one as OPAC-visible.
5. Repeat the CONS-level SRU search, including holdings. The record
   appears in search results, but holdings information in 852 includes
   *all* copies, including non-OPAC-visible copies.

Signed-off-by: Jeff Davis <jdavis@sitka.bclibraries.ca>
Signed-off-by: Kyle Huckins <khuckins@catalyte.io>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>