Resolve "MR refactor: Disable toggle comments button when diff has no discussions"

What does this MR do?

Disables toggle comments button when diff has no discussions Vertically aligns buttons with svgs in file header

Screenshots (if relevant)

before	after

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conform to the code review guidelines
  • Has been reviewed by a Frontend maintainer
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them

What are the relevant issue numbers?

Closes #49161 (closed)