Re-add swap revisions feature (legacy)

What does this MR do?

This re-adds the "Swap revisions" button to the legacy revision compare view.

The "Swap revisions" button for the redesigned compare view (currently behind a FF) will be done in a separate MR.

TODO

• Update legacy compare view
• Update redesigned compare view (follow-up MR)

Screenshots (strongly suggested)

before	after

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Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
• Code review guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Related to #225345 (closed)