Controlled forms and inputs should always have a `value`

[jho406]

When using the controlled options

  form_props(controlled: true, model: Post.new) do |f|
    f.text :title
  end

The output does not contain a value

      "inputs": {
        "title": {
          "type": "text",
          "name": "post[title]",
          "id": "post_title"
        },

This poses a problem in react land because if there suddenly is a value, react will say something to the effect of "uncontrolled component suddenly becomes controlled". So if controlled is used anywhere, we should give it a default value of nil or maybe empty "". I'm not sure which one makes the most sense, and would love some opinions.

[jho406]

The only wrench to this is, when f.select has multiple: true, the value default (with controlled: true) should be an empty array.