Block Style States: Add @current custom state for Nav Link

[MaggieCabrera]

What?

Closes #38277. Part of #77817.

Adds the @current state to Block Style States so a user can style the active menu item for core/navigation-link, in the block inspector and in Global Styles. Third state axis after pseudo (#76491) and responsive (#78384), and the first custom (class-based) state to ship.

Why?

Until now, theming the current menu item meant hand-writing theme.json or custom CSS. @current is the canonical use case for a class-based state, WordPress applies .current-menu-item at render time when a link's URL matches the request.

How?

• selectors.states["@current"] on navigation-link/block.json is a class fragment (.current-menu-item), not a full selector. Both consumers compose it under the block's root selector via append_to_selector().
• Adds an "Item" group to the State dropdown alongside Viewport and Pseudo state; wires the new field end-to-end through the store, path-builder, block inspector, and Global Styles screen.
• Extracts StateMenuGroup so the three dropdown groups share one source of truth.

Selector shape (kept-on-purpose tradeoff, #75736)

The team split on @current's CSS shape: @scruffian preferred the broad .wp-block-navigation .current-menu-item; @talldan preferred the narrow .wp-block-navigation-link.current-menu-item. This PR lands on talldan's form. Side effect: the Global Styles output shape for @current changes. Needs Dev Note.

Not in this PR

• Nav Link color/border/spacing supports — separate branch add/nav-link-style-supports. Until that lands, only typography is visible under @current in the block inspector. Global Styles is unaffected (it exposes the full panel).
• JSON schema docs for selectors.states — follow-up.
• Public block.json opt-in for third-party blocks — still deferred per Update state support to use config instead of block supports #78088.

Testing Instructions

1. Open the site editor → Styles → Blocks → Custom Link.
2. Open the States dropdown in the header → Item → Current.
3. Set any supported style (e.g. Typography → Font size → Large).
4. Save Global Styles.
5. Publish a Page with a Navigation block whose Custom Link points to the Page itself; visit the Page. The current menu item renders the styled rule.

Screenshots

States dropdown on Global Styles:

Frontend:

Use of AI Tools

Authored with Claude Code (Opus 4.7). All output reviewed and validated by the author.

[github-actions]

Size Change: +801 B (+0.01%)

Total Size: 8.44 MB

📦 View Changed

Filename	Size	Change
build/scripts/block-editor/index.min.js	381 kB	+680 B (+0.18%)
build/scripts/block-library/index.min.js	324 kB	-4 B (0%)
build/scripts/edit-site/index.min.js	296 kB	+47 B (+0.02%)
build/scripts/editor/index.min.js	466 kB	+78 B (+0.02%)

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[github-actions]

Flaky tests detected in 4223a4b.
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/27193382063
📝 Reported issues:

• [Flaky Test] shouldn't conflict with server-side autosave #78706 in /test/e2e/specs/editor/various/autosave.spec.js