Open staged files from Web IDE right sidebar

What does this MR do?

Enables users to click the staged file paths on the Web IDE right sidebar to (re)open them on the editor.

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

"WIP" refers to me struggling to make the vue component test a bit less shallow and test that the router was also called. Will still give it a shot, but any ideas/guidance is appreciated.

Why was this MR needed?

It would be really handy if files could be opened from the commit panel. This would mean that if I close a file I have changed I can quickly re-open it without having to navigate a large file tree. from #4572 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• 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
• Internationalization required/considered No.

What are the relevant issue numbers?

Closes #4572 (closed)