Simplify usage of colors and icons in file browser

This is an actionable insight from the UX Department: MRs experience async critique research (insight).

What

There are many different icons and colors in the merge request file browser, which raise some problems/questions:

1. The file status icons can be ambiguous.
   • Related to this, Gerrit recently changed from using letters (e.g. A for Added) to spelling it out completely and no longer shows the “Modified” status (example).
2. Do we need to show -0 and +0 if there are no removed or added lines respectively?
   • See this interesting thread with some proposals: #118442 (comment 273409654)
3. Do the file type icon colors help? Or would they still work as well if they were monochromatic?

Why

The current experience of the file browser can be overwhelming and confusing, trying to communicate a lot of different things in a small space.

How

Research how it would be possible to reduce and simplify the usage of colors and icons in the file browser.