IIIF manifests: revisit how attribution (v2) and requiredStatement (v3) are populated

[anarchivist]

Requested by Ben A.:

The TL/DR is that the attribution statement in our manifests doesn't actually provide an attribution statement - looks like it's just the applied license, which probably should go in the "license" field instead. For a visually-focused client like Mirador, the SUL logo at least lets users know the source institution, but it probably doesn't satisfy the goal of an attribution statement.

My understanding of current state:

The attribution/requiredStatement values in PURL are currently drawn from 1) the human-readable copyright statement in the publicXML; 2) for CDL items, additionally a CDL-specific copyright statement; 3) a fall back to a static “Provided by the Stanford University Libraries” if neither exist/are applicable. Could we verify what we actually want to display in these cases?

We could, perhaps, populate attribution/requiredStatement with additional information from copyright/useAndReproduction data in the publicXML, but specific requirements are not yet clear; this is subsequently blocked until we can iron that out.

See also #472.