Resolve "Select branch dropdown is too close to branch name"

What does this MR do?

Fixes the margin between the branch selector and the breadcrumbs by reusing the same structure and css classes that were already reused from the tree section :

Also it fixes the mobile view :

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

• Reuse of Structure + CSS ok ? Otherwise we end up with tiny small classes for each tiny thing

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #34349 (closed)