Menu: MenuFooter children excluded from arrow-key navigation

Description

Children placed inside MenuFooter (e.g., a "Browse" button) are excluded from the Menu component's roving tabindex arrow-key navigation. Users can Tab to reach MenuFooter items, but arrow keys skip over them entirely.

This breaks the expected keyboard pattern where all interactive items within a menu are reachable via arrow keys.

WCAG Impact

• 2.1.1 Keyboard — All interactive elements within the menu should be reachable via the menu's keyboard navigation pattern (arrow keys)

Steps to Reproduce

1. Create a Menu with several MenuItem entries and a MenuFooter containing a Button
2. Open the menu and use arrow keys to navigate
3. Observe that arrow keys cycle through MenuItem entries but never reach the MenuFooter button
4. The MenuFooter button is only reachable via Tab, which exits the menu's roving tabindex pattern

Expected Behavior

Arrow-key navigation should include MenuFooter children as the last item(s) in the navigation sequence, or there should be an opt-in mechanism to include footer actions in the roving tabindex.

Context

We use MenuFooter to place a "Browse" action inside select dropdowns (e.g., PageFormAsyncSingleSelect in ansible/ansible-ui). Keyboard users cannot reach the Browse button via arrow keys, only via Tab — which is inconsistent with the rest of the menu's keyboard model.

Jira Issue: PF-4544

まず Menu および MenuFooter コンポーネントの実装と、それらのキーボードナビゲーションのテストを見つけ、次に MenuItem エントリとフッターの Button を使って報告された挙動を再現します。roving tabindex の項目がどのように収集されるかを追跡します。フッターの children が矢印キーによるナビゲーションに参加し、テストで期待される順序をカバーできれば完了です。