Support orientation property in Menubar

[YuChuHB]

Description

Support orientation property in Menubar to support vertical display. Its default value is horizontal, and also supports vertical.
Below is the behavior comparison:

Behavior	horizontal	vertical
Navigation	ArrowLeft and ArrowRight	ArrowUp and ArrowDown
Open Menubar Content	ArrowDown	ArrowRight
Navigation when Menubar Content is open	The new navigated menu's content is auto open	Cannot navigate when Menubar Content is open

Note: When Menubar Content is open, besides disabling navigation, press ArrowLeft also cannot close the Menubar Content, since I find for horizontal case, we also cannot use ArrowUp to close the Menubar Content. Not sure it is acceptable or not.

I am a newer to Radix Primitives, and not sure whether there are anything I missed to change. For example, How do we update the documentation in the official website https://www.radix-ui.com/primitives/docs/components/menubar ?

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Latest commit: fc0118a

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[YuChuHB]

@benoitgrelard @chaance Can you help review this PR to see whether it can be merged? Thanks.