Multi File Editor File icons

What does this MR do?

Adds based on file names + file endings Icons to the Files displayed in the Multi File Editor. Folder Icons are still the same GitLab specific ones.

We discussed in the last Editor Call to move now forward with it just for the editor and not the rest to keep it iterative.

EE-Port : gitlab-org/gitlab-ee!3873

Why was this MR needed?

To make files much easier to understand

Screenshots (if relevant)

(Ignore the folder icons of this screenshot)

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

#37624 (closed)