Update icons on file viewer

[dbranchini]

New design for the file viewer included new icons to sul-embed, @justinlittman suggested moving this into a separate ticket. He mentioned that they are currently using their own font for icons, so this might be a larger question regarding which icon library we should be using across all viewers (or, even better, across all SUL apps).

See #1849 and https://www.figma.com/proto/LVP13xZ0HhrxAPHCnoMVW1/Embedded-File-Viewer?page-id=0%3A1&type=design&node-id=316-1113&viewport=-2703%2C-153%2C0.5&t=drUPK0C4xcXsgdsS-1&scaling=min-zoom&starting-point-node-id=316%3A1113&mode=design for reference.

[thatbudakguy]

I think we should keep this specific to the file viewer for now. The issue of consistency of icons across apps would probably involve decisions about https://github.com/sul-dlss/sul_styles and how it's used, and I don't know much about how that works or why it exists in the first place.

If the material design libraries we're including in sul-embed currently provide icons (I think they do, because I think the media team is using these icons on the new media viewer) then we should presumably use that same icon set for changes to any of the other viewers, at least for now. I think it's this icon set.

[dbranchini]

Decided that the current icons are not a problem for accessibility or usability, so we will backlog this item until we can have a more thorough discussion about a single font library for SUL web properties.