Keep merge request button height consistent for small viewport width

What does this MR do?

Wraps certain buttons (or anchors with role="button") in the merge request widget with spans. This prevents the button height from filling the entire container height. In some cases, like when the viewport width is very small, the container height can be large, making the buttons large and ugly. This MR keeps the "buttons'" height consistent.

There might be other "buttons" in the MR widget that need this treatment.

This is an improvement on !17283 (closed).

/cc @fatihacet

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

Why was this MR needed?

See #42746 (closed), https://gitlab.com/gitlab-org/gitlab-ce/issues/42677

Screenshots (if relevant)

Before

After

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-qa manual pipeline job)

What are the relevant issue numbers?

Closes #42746 (closed) Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/42677