feat: Introduce Popover.Context and onOpen handler

[Newbie012]

Adds Popover.Context, a render-prop component providing access to the popover context, including new onOpen. This allows custom state control while still using built-in components. I also Included documentation and a test case for hover behavior.

Example:

<Popover>
  <Popover.Target>
    <Popover.Context>
      {({ onOpen, onClose }) => (
        <button type="button" onMouseEnter={onOpen} onMouseLeave={onClose}>
          test-target
        </button>
      )}
    </Popover.Context>
  </Popover.Target>

  <Popover.Dropdown>
    <div>test-dropdown</div>
  </Popover.Dropdown>
</Popover>

[shwu-jt]

I think we can make <Popover> to take ReactNode | (args: {onOpen, onClose}) => ReactNode instead so we don't need another layer of <Popover.Context>.