TopBarMenu does not close on blur or select

When selecting an item or programmatically shifting focus causing a `blur` event, the [`TopBarMenu` component](https://cauldron.dequelabs.com/components/TopBarMenu) remains open and the focus indicator for that element does not reappear on focus until the component is clicked again.

- `onBlur` for the containing element should cause the menu to close.
- Selecting an item in the menu should also cause the menu to close.
- It would also be nice to expose the Close method as either a prop or as a React hook