Provide adapter for formstate

[nighca]

README

https://github.com/nighca/formstate-x/blob/adapter/src/adapter/README.md

Usage

import * as fs from 'formstate'
import { FormState } from 'formstate-x'

// the adapt method
import { xify } from 'formstate-x/esm/adapter'

// formstate FieldState or FormState
const stateA = new fs.FieldState(1)
const stateB = new fs.FormState({ ... })

// formstate-x FormState
const formState = new FormState({
  a: xify(state),
  b: xify(stateB)
})