Resolve "Merge request refactor displays changes dropdown incorrectly"

What does this MR do?

Resolves "Merge request refactor displays changes dropdown incorrectly"

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

Why was this MR needed?

#48497 (closed)

Screenshots (if relevant)

Before	After

Dropdown behaviour

Current Behavoir	New Behavoir
The dropdown only opens in one direction (downwards) regardless of the amount of space around it screencast_2018-06-28_16-17-16	The dropdown opens in whichever direction has more space both upwards and downwards screencast_2018-06-28_16-07-37

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
• 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 #48497 (closed)