Fix ref on root component pointing to internal component

[eps1lon]

When using mount(<div ref={React.createRef()} />) ref.current was pointing to an internal wrapper component.

Previous workarounds:

1. mount(<><div ref={React.createRef()} /></>)
2. mount(<div />).instance()

Both workarounds require knowledge of either enzymes API (2) or internals (1). Making this just™ work should be preferred IMO.

[eps1lon]

When I opened this I didn't realize how many moving parts are involved for this. Since this already has two workarounds I'm not that motivated to spend more hours on this fix.

Since I won't work on this I'm closing for now. Feel free to reopen and finish the work required to get this merged.