In-editor revisions: Show title and excerpt changes in the revisions sidebar

[priethor]

What

Follow-up to this comment on #80314.

The existing Meta panel is renamed to Fields to also show Title and Excerpt alongside the meta rows, with word-level diffs when either value changes. Title and Excerpt only appear when their values differ.

Why

Restoring an older revision can replace the post title and excerpt. Until now, neither change appeared in the comparison before clicking Restore.

How

The shared diff panel can now receive its open state from a caller. Selecting a revision with a Title or Excerpt change opens Fields. Selecting one without those changes leaves the panel alone, so an open meta comparison such as footnotes does not suddenly collapse. The block attributes panel continues to manage its own state.

Testing Instructions

1. Create a post with the title First title, the excerpt First excerpt, and a footnote containing alpha. Save it.
2. Change the title to Second title and the excerpt to Second excerpt. Add a footnote containing beta, then save again.
3. Add a third footnote containing gamma without changing the title or excerpt, then save once more.
4. Open the revisions screen. Open Fields, check that Title and Excerpt are not listed for the latest revision, and confirm that the footnotes row contains gamma. Close Fields.
5. Move to the previous revision. Check that Fields opens on its own and shows the Title and Excerpt diffs. Return to the latest revision and check that the panel stays open while the Title and Excerpt rows disappear.

---

I used Claude to help implement these changes. I guided the work, then tested and reviewed the result.

[github-actions]

Size Change: +160 B (0%)

Total Size: 7.82 MB

📦 View Changed

Filename	Size	Change
build/scripts/editor/index.min.js	510 kB	+160 B (+0.03%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in acc8d07.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/31169158199
📝 Reported tests:

should load styles added through enqueue_block_assets in /test/e2e/specs/editor/plugins/iframed-equeue-block-assets.spec.js, passed after 1 failed attempt.

[github-actions]

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Co-authored-by: priethor <priethor@git.wordpress.org>

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