feat: add vertical/horizontal orientation option in menu

[sayers24]

🙋 Feature Request

I noticed the menu/menu-item components have keyboard navigation listeners that assumes vertical navigation for a top-level list of items and right-arrow to open sub-menus. I have a case where a menu is laid out in a horizontal fashion. Very similar to the scenario W3C describes where Web application menus are expected to work like desktop application menus

🤔 Expected Behavior

W3C app menu spec - When horizontal layout is specified, left/right arrows nav between top level items, down arrow opens sub menu, up arrow closes sub menu

😯 Current Behavior

Vertical layout is assumed where up/down arrows nav between top level menu items, right arrow opens sub menu

💁 Possible Solution

Add an orientation option to support pivoted keyboard actions

🔦 Context

Context listed above

💻 Examples

fast's vertical menu (Nested option)