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

首先定位 Menu 和 MenuFooter 组件的实现及其键盘导航测试，然后使用 MenuItem 条目和一个 footer Button 重现报告的行为。跟踪如何收集 roving tabindex 项。完成标准是 footer 子项参与方向键导航，并且测试覆盖预期的顺序。