When loading a review request with file attachments, we'd show a spinner

with a little status message, and eventually replace it with loaded file

attachment data as soon as the JavaScript had finished executing. We

have it this way in order to avoid duplicating a lot of file attachment

setup logic in the template.
This ultimately led to a fairly annoying page jump on load, and wasn't

particularly pleasant from a user's point of view.
This change implements a sort of half-way version of this. We now

display placeholders for each thumbnail, just the box for the attachment

without any thumbnail or identifying information. This is displayed

faded out, and a new-style spinner is displayed next to the "Files"

header, making it clear that we're still loading.
Accessibility hints were added so that screen readers can be aware when

the attachments area is still in the process of loading and when it has

finished.

Loaded a page with file attachments. Saw that there was a placeholder

thumbnail for each of the attachments, which were then replaced with the

real ones.
Checked the accessibility states before/after load.