Responsive title in diffs inline, side by side, with and without sidebar

What does this MR do?

Makes the file name in MR diffs responsive when:

• Diff is side by side and the sidebar is closed
• Diff is inline and the sidebar is closed
• Diff is side by side and the sidebar is opened
• Diff is inline and the sidebar is opened

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • 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 #25709 (closed)