Toolbar: Add access+w keyboard shortcut to toggle toolbar on frontend

[apermo]

Add a keyboard shortcut (Ctrl+Shift+F) to temporarily hide and show the toolbar on the frontend. This gives logged-in users a quick way to preview their site without the toolbar, without navigating to Profile settings or logging out.

Shortcut: Ctrl+Shift+F (all platforms)

Behavior

• Toggle only: Hide the toolbar; press again to bring it back.
• No persistence: Resets on page navigation — designed for quick previews.
• Frontend only: Does not work in wp-admin (toolbar is not optional there, see #19685).
• Smooth animation: 200ms CSS transition (slide up/down).
• Page spacing adjusts: Sets --wp-admin--admin-bar--height: 0px when hidden, so scroll-padding-top and bump margin-top adjust automatically.
• Accessible: aria-live region announces state changes; aria-hidden set on the toolbar element.

Changes

1. src/js/_enqueues/lib/admin-bar.js — keydown listener for Ctrl+Shift+F, toggleToolbar() function, screen reader announcements.
2. src/wp-includes/css/admin-bar.css — html.wp-toolbar-hidden rules: CSS variable reset, margin override, transform: translateY(-100%) + visibility: hidden.
3. src/wp-includes/class-wp-admin-bar.php — wp_localize_script for screen reader strings.

Shortcut rationale

Ctrl+Shift+F was chosen after evaluating and discarding several alternatives:

• access+w (Ctrl+Option+W / Alt+Shift+W): Initial choice. Discarded because Ctrl+Option on macOS conflicts with the accessibility Display zoom modifier, and Alt+Shift on Windows switches keyboard input language on multi-language setups.
• Ctrl+Shift+H: "H for Hide" — discarded because Firefox uses Ctrl+Shift+H for the History sidebar.
• primaryShift+\ (Cmd+Shift+\ / Ctrl+Shift+): Matches Gutenberg's distraction-free mode shortcut. Discarded because \ is not directly accessible on non-US keyboard layouts (e.g. German keyboards require Alt+Shift+7).

Ctrl+Shift+F is free across all major browsers (Chrome, Firefox, Safari, Edge) on all platforms, works on every keyboard layout, and follows the ctrlShift modifier pattern already used in WordPress for region navigation. "F" is mnemonic for "Frontend view."

Prior Art

This PR is based on the keyboard toggle feature from Apermo AdminBar (GitHub) by @apermo. The toggle is also available as a standalone lightweight version: Apermo AdminBar Toggle. The human author of this PR is the plugin author.

Trac ticket: https://core.trac.wordpress.org/ticket/65029

Use of AI Tools

This PR was authored collaboratively with Claude Code (Anthropic Claude Opus 4.6). The AI was used for:

• Research: Auditing existing WordPress keyboard shortcuts, browser shortcut conflicts, and Trac history for prior proposals.
• Implementation: Writing the JavaScript toggle logic, CSS hidden state rules, and PHP localization. All code was reviewed and directed by the human author.
• Trac ticket draft: The ticket description was drafted by AI and reviewed by the human author.

The human author (@apermo) is also the author of the Apermo AdminBar / Apermo AdminBar Toggle plugins that this PR is based on. All code has been reviewed and the human author takes full responsibility for the contents of this PR.

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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.

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