Resolve "Improve performance of MR Changes tab: reduce event listeners on scroll event"

What does this MR do?

Removes the scroll event listeners than handle showing the file path next to the dropdown changes. Falls back to the design before the refactor with the dropdown and the number of changes only.

• Removes scroll event listeners being added to each file
• Adds back the number of additions/deletions to the right top corner
• Increases the size of the dropdown caret in the changed files dropdown

Screenshots (if relevant)

10.8	production	this MR
10.8		remove_scroll

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• Conform by the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #48639 (closed) Closes #48789 (closed)