Ide lock files

What does this MR do?

It makes locked files visible + usable in the Multi File Editor:

• Icon in Sidebar
• Icon in Tab
• Read Only Mode in Monaco for locked files

Are there points in the code the reviewer needs to double check?

New Karma Tests for testing Monaco Editor

Why was this MR needed?

To make locked files usable in the Multi file editor.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

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

What are the relevant issue numbers?

closes #3918 (closed)