[context menu] `Sub` root part

[atomiks]

Currently, it's not possible to disambiguate a submenu and a new root menu that's nested in the React tree while reusing the ContextMenu namespace.

This is more obvious/clear with a ContextMenu than a regular Menu, because they can easily be nested.

As a result of a missing .Sub or .Subroot part, the current API requires you use Menu to create a submenu, rather than additional parts directly on ContextMenu:

<ContextMenu.Root>
  <ContextMenu.Trigger>
    <ContextMenu.Root> {/* this is a new root, not a submenu *}
      ...
    </ContextMenu.Root>
  </ContextMenu.Trigger>
</ContextMenu.Root>

While it may only apply to ContextMenu in most cases, for consistency, it may be better for all Menu components to work the same

[github-actions]

This feature will be available in the next npm release of Base UI.

In the meantime, you can try it out on our Canary release channel:

npm i https://pkg.pr.new/@base-ui-components/react@2042