When a form is valid the output is a tree of Value
items that represent the type and value of each field or group/list of fields in the form.
type Value = IntValue Basics.Int
| FloatValue Basics.Float
| StringValue String
| BoolValue Basics.Bool
| ListValue (List Value)
| ObjectValue (List ( String, Value ))
| NullValue
| EmptyValue
| JsonValue Json.Decode.Value
A form value.