Bug 20244: Add alt script indexing and fix sort field indexing

Bug 20244: Add alt script indexing and fix sort field indexing

https://bugs.koha-community.org/show_bug.cgi?id=20244

Test plan:

1. Add a record with alternate script fields in 880 (sample attached in the bug).
2. Make sure the the record can be found e.g. with the alternate script title.
3. Add a record with multiple authors.
4. Check that in the index there is only a single author__sort field.

Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>