Introduce cascading menus for actions

[marcoambrosini]

I think the the current submenu UX is not ideal and should only be a mobile fallback. We should have proper cascading menus for devices that are big enough. This allows to very quickly scan the content of the submenus and removes the clumsy mouse interaction of going one level deep and coming back.

Examples

Microsoft 365

Google drive

Slack

Zoom

Originally posted by @marcoambrosini in https://github.com/nextcloud-libraries/nextcloud-vue/issues/6209#issuecomment-2473048317

[ShGKme]

Discussed again in the design call.

The current decision:

1. For the desktop use the cascade menu, like in other desktop apps and web-apps with multi-level menus
2. For the mobile we have 2 options:
   1. Keep the current solution with opening the next menu and the "⬅️ Back" button (example: Signal)
   2. Use a bottom sheet like mobile apps

[marcoambrosini]

@ShGKme for mobile as a first step we decided to go with i