Fixed empty editors in the IDE

What does this MR do?

Fixes 2 different cases where the IDE editor could end up blank.

1. When the user switches to commit mode after a change & then tries to re-open the staged/unstaged change. This was caused by re-adding a pending that was already opening which meant the editor wasn't recreated after the model was disposed.
2. When the user comes from a merge request, edits the file & switches between modes. This was caused by the file being added with the wrong URI. Instead of using file.path it should of been using file.key.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• 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
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #46153 (closed)