[Menu] ARIA APG: Disabled menu items should be focusable with keyboard navigation

Duplicates

• I have searched the existing issues

Latest version

• I have tested the latest version

Current behavior 😯

1. Enter into a Menu with a disabled item
2. Use keyboard to navigate Menu
3. Observe that disabled items cannot be focused

Expected behavior 🤔

1. Enter into a Menu with a disabled item
2. Use keyboard to navigate Menu
3. Disabled items can be focused
4. Disabled items cannot be activated

Steps to reproduce 🕹

Steps:
https://codesandbox.io/s/mui-disabled-menu-item-keyboard-navigation-8k3rwl

1. Move focus into Menu
2. Use keyboard to navigate
3. Observe behaviour

Context 🔦

According to APG menu/menubar pattern[1], disabled menu items should be focusable but cannot be activated (see "NOTE" in [1]).

The APG menu button pattern[2] does not override these requirements, and instead specifies that the specifications of Menu/Menubar should be followed after a menu is opened.

[1] https://www.w3.org/WAI/ARIA/apg/patterns/menu/
[2] https://www.w3.org/WAI/ARIA/apg/patterns/menubutton/

Start by reproducing the behavior in the linked CodeSandbox and trace the Menu keyboard-navigation implementation. Check the existing Menu behavior and tests, then ensure disabled items receive keyboard focus without activation; done means navigation reaches them while activation remains blocked.