feat: #3582576 Add preview link to Navigation top bar.

Arthur Lorenzrequested to merge
issue/lupus_decoupled-3582576:3582576-add-preview-in into 1.x

Add a 'Preview in new tab' link to the responsive preview top bar on layout builder pages. Extends ResponsiveIcons from responsive_preview_navigation via hook_top_bar_item_alter.

Includes LegacyHook fallback for Drupal 10 compatibility and a class_exists guard so the module works without responsive_preview_navigation installed.

Closes #3582576

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