Make FOLIO item sort configurable.

[demiankatz]

This PR adds a config setting to control the sort order of items within holding locations. It defaults to using volumes. Note that this is imperfect, as it uses an ASCII-based sort that will sort "100" before "90", etc. However, even with that limitation, it is an improvement on the completely random order we otherwise get. It could be augmented in future with additional settings to apply custom sorting in VuFind after the data has loaded.

[demiankatz]

@bbusenius, I'm interested to know how you're dealing with this situation at UChicago...

[bbusenius]

Hi @demiankatz, for this we just do a usort before we return everything. If the holding is a serial, we return it in reverse order. It's likely not very efficient but this is something that people were very particular about at our institution. Ours does not give perfect results but it has been deemed good enough for the most part. https://github.com/uchicago-library/vufind/blob/uc-master/module/UChicago/src/UChicago/ILS/Driver/Folio.php#L360

[demiankatz]

Thanks, @bbusenius! I've revised this PR so it now offers two options: you can configure folio_sort to perform a sort on the FOLIO side using native capabilities, or you can configure vufind_sort to do a post-processing sort within VuFind. I think this should address most use cases one way or another. What do you think?

Also note that this changes the way VuFind generates copy numbers so that each holding location has its own numeric sequence; I think this probably makes more sense than the previous approach (though the change comes mostly as a side effect of refactoring rather than as a conscious design decision).

[demiankatz]

@bbusenius, I also wonder if it might be valuable to refactor this very long method a bit so that there's a support method that formats a single item record, and another support record that formats a single holdings record... This will not only improve readability but also enable custom code like yours to be more narrowly targeted. Do you think that's worth doing here, or as a follow-up?

[bbusenius]

I had forgotten that since we use enumeration and copy number for the number field, we don't need to renumber them. I think the new numbering sequence is fine. I really like how this offers both pre and post sort options. I do like the idea of separate support methods for item and holdings formatting but I would probably do it as a follow-up since it's not directly related to the sorting.

[demiankatz]

Thanks, @bbusenius -- if you can give me an approval on this PR, then I can merge this and open a follow-up to refactor as discussed. (Of course, if there's anything here you don't feel comfortable approving, or if you'd like to get more eyes on this first, let me know and we can discuss/ask for more input first).

[bbusenius]

This looks good to me! Thanks for taking us into consideration with the post sort!

[demiankatz]

Thanks, @bbusenius, I'll get to work on the refactoring as soon as time permits. :-)