WIP: Multi file blob viewer

What does this MR do?

Adds the ability for files to display rich viewers in the multi-file editor. With this it is also possible to switch between rich viewer & simple viewer. The rich viewer is loaded by default, if there is no rich viewer then the simple viewer is loaded.

In this iteration all the viewers are requested from the backend, in the next iterations some viewers (pdf, stl etc.) will be rendered 100% on the frontend without requesting the backend for HTML.

Screenshots (if relevant)

What are the relevant issue numbers?

Closes #38355 (moved)