Allow parameter value modification from a Story code

[eymar]

For example:

val `Checkbox` by story {
    val checked by parameter(false)
    Checkbox(checked = checked, onCheckedChange = {
        checked = it // not possible because property delegate doesn't have setValue method
    })
}

One of the solutions might just be to accept a mutableState which would be used both in Story/Composable code and in modifiable Story parameters.