Ensure that viewers show rather than thumbnails

[laritakr]

Story

Refs:

• PDF.js not rendering when it should #880
• UV not rendering when it should #881

In the case of a split work, :pdf? needs to be included in the methods checked on a presenter.
In the case of a work that isn't split, Valkyrie has changed the term we use to check for a .pdf suffix. It appears that we do not fill in the label term. If characterization fails and we fall back to looking for a pdf, we needed to look in the right location.

Expected Behavior Before Changes

When PDF.js is selected via flipper and a work has been split, it sometimes just shows a thumbnail.
When PDF.js is selected via flipper and work is not split, it sometimes just shows a thumbnail.

Expected Behavior After Changes

In new (valkyrie) resources, resources converted from Fedora, and works still in Fedora:

• When PDF.js is selected via flipper and a work has been split, it shows the UV
• When PDF.js is selected via flipper and a work is not split, it shows the PDF in PDF.js

Screenshots / Video

Both of these originally showed thumbnails only

Notes