[BUG] OAI-PMH workaround for Linked Agent fields no longer works.

[rosiel]

What steps does it take to reproduce the issue?

I spun up a fresh Playbook and added a Book record with some metadata. The author, who I entered in a Linked Agent field, isn't displaying in the OAI-PMH record.

• When does this issue occur?
  When looking at records through OAI-PMH

• Which page does it occur on?
  http://localhost:8000/oai/request?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai:localhost:node-1 (in my case)

• What happens?
  no linked agent.

• To whom does it occur (anonymous visitor, editor, administrator)?
  probably everybody

• What did you expect to happen?

This code would imply that the author should appear. Documentation is a little vague but implies the same.

The problem appears to be that sometime in the last three years, @joecorall refactored the REST OAI-PMH module to no longer use a theme hook, so our preprocess function isn't running. Here's the theme function in a commit from 2 years ago, but the .module file doesn't declare hook_theme() anymore.

Which version of Islandora are you using?
Playbook, 2.x branch

Any related open or closed issues to this bug report?

Screenshots:

[rosiel]

This should be updated in the plugin in the OAI PMH modle