Add wrapper around createRef with atom protocols

[lilactown]

Example usage:

(let [ref (helix.core/ref nil)]
  (reset! ref "foo")
  (prn @ref) ;; => "foo"
  (set! (.-current ref) "bar")
  (prn @ref) ;; => "bar"
  )

[rome-user]

I am experimenting with an implementation of this, but do we really want to add this?

The createRef is only really useful in class component, but that is rather awkward to use in Helix IMO, for three reasons:

1. defcomponent makes several assumptions about state
2. Class components cannot use hooks
3. defcomponent does not have a clj-kondo linter, so one needs to ignore it or use def-catch-all, which is a worse DX than defnc.

[lilactown]

We found it useful when doing some interop between reagent and helix, where we needed to create a ref in a reagent component and pass it to a helix component. I agree that it shouldn't be used except in niche scenarios like that.