Menu should close and move to next focusable element on <Tab>

[eriese]

Fix for #1634

Current behavior is that user cannot tab away from menu. According to the WAI ARIA Menu pattern, Tab key behavior should be as follows:

Tab and Shift + Tab:
Move focus into a menubar:
If focus is moving into the menubar for the first time, focus is set on the first menuitem.
If the menubar has previously contained focus, focus is optionally set on the menuitem that last had focus. Otherwise, it is set on the first menuitem that is not disabled.
When focus is on a menuitem in a menu or menubar, move focus out of the menu or menubar, and close all menus and submenus.
Note that Tab and Shift + Tab do not move focus into a menu. Unlike a menubar, a menu is not visually persistent, and authors are responsible for ensuring focus moves to an item inside of a menu when the menu opens.

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Name	Status	Preview	Updated
headlessui-react	✅ Ready (Inspect)	Visit Preview	Jul 2, 2022 at 8:16PM (UTC)

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[RobinMalfait]

Hey! Thank you for your PR!
Much appreciated! 🙏

I continued on your work here #1673 and will be available in the next release.

You can already try it using:

• npm install @headlessui/react@insiders.
• npm install @headlessui/vue@insiders.