Example use case:

```tsx
// Some components have this API with an `innerRef`. The suggested approach is to use
// `React.forwardRef` so that you get the actual `ref` value. However if you already have this
// `innerRef` API than we can use the `refName="innerRef"` to give the `ref` prop a good name. It
// defaults to `ref` so that it still works everywhere else.

function MyButton({ innerRef, ...props }) {
  return <button ref={innerRef} {...props} />
}

<Menu.Button as={MyButton} refName="innerRef" />
```

+ use the unique __ symbol as a default value in the Props type for the
  omitable props.

… render strategy