Revisions: Clarify revision comparison and restore states

[Sukhendu2002]

Trac ticket: https://core.trac.wordpress.org/ticket/61447

This PR clarifies the Revisions screen so users can more easily identify which versions are being compared and which revision can be restored.

It:

• Displays both the From and To revision details by default.
• Replaces the disabled restore button for the current revision with “This is the current version.”
• Hides the empty From row when viewing the earliest revision.
• Renames Previous and Next to Earlier and Later.
• Adds unique author-information IDs for accessible slider labels.
• Correctly maps From and To slider labels in RTL mode.
• Updates the pinned, tooltip, and responsive layouts.
• Updates the Revisions help text.

Testing Instructions

1. Create and publish a post.
2. Update the post at least twice to create multiple revisions.
3. Open the Revisions screen for the latest revision.
4. Confirm both From and To revision details are displayed.
5. Confirm the latest revision says “This is the current version” instead of showing a disabled restore button.
6. Select Earlier and Later and confirm navigation works.
7. Confirm a non-current revision displays an enabled Restore This Revision button.
8. Navigate to the earliest revision and confirm no empty From row appears.
9. Enable Compare any two revisions and confirm both slider handles work.
10. Repeat the comparison using an RTL site language and confirm the handles have the correct From and To accessible labels.
11. Test at desktop and mobile viewport widths.

Use of AI Tools

AI assistance: Yes
Tool(s): OpenAI Codex
Model(s): GPT-5.6
Used for: Ticket analysis, initial code skeleton, accessibility review.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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