feat: make Fable.Form.Simple pluggable

[MangelMaxime]

Beta versions are already out, so you can give it a try 🎉

• Fable.Form - 3.0.0-beta-001
• Fable.Form.Simple - 5.0.0-beta-001
• Fable.Form.Simple.Bulma - 5.0.0-beta-001

Upgrade form previous version:

1. Change Form.Form<Values, Msg, _> = or Form.Form<Values, Msg, IReactProperty> = to Form<Values, Msg> =

2. Add FieldId = "replace-me" to all the attributes that fails to compile.

   FieldId should be unique across your form

If you want to create a custom field you can looks at:

• CheckboxField - Showcase how a standard field looks (simple code)
• SignatureField - Showcase how you can make a more complex field (showcase using a ReactComponent)

API is not final yet, but looking at how things went I don't think the expose API will change too much. 🤞

---

Would be nice to have done before making a stable release:

• Update the documentation
  • Keep a reference to old documentation if possible by copy/pasting files
  • Explains how to create a custom field
• Explore exposing an attributes builder API to avoid having to defined empty list or default values when we don't want to. It also allows to add new features to Attributes without breaking the user code because such new features will have a default value. For example, if we add Add help policy #26
• Add Base.disableIf  #45
• Add IsLoading to the field config #44 (look what can be done here)
• Add help policy #26
• Look into using Fable.Form for FuncUI to check what could be done
• Looks into removing Elmish dependency to make Fable.Form more flexible (related to Explore if Fable.Form can be used with React hooks #21)
• Look into making Fable.Form.Simple renderer agnostic
• Add readOnly support (it works similarly to disable)
• Add an example, of how to use Record to store the field state instead of just a primitive (could be an autocomplete text for example, to have a show/hide boolean for the list of choices)
• Add an example of using a record for handling the value of a field instead of just a primitive
• Look to make select, option, etc. works with any types and not just (string * string)
• Showcase, how one can customise the rendering of a field

Won't do:

• Look into using TypeScript to create a field

  After looking into it, it is in theory possible to use TypeScript to create field. But it requires, access to the generate code by Fable.

  The reason, is that even if most of the new API is testing things by the shape of it. Some of the API needs to call internal API:

   let form<'Values, 'Field, 'Output>
       : ((InnerField<'Values> -> 'Field)
             -> Base.FieldConfig<Attributes, string, 'Values, 'Output>
             -> Base.Form<'Values, 'Output, 'Field>) =
       Base.field String.IsNullOrEmpty
       
       // Base.field cannot be shadowed because it is the hearth of Fable.Form

  Things like StandardRenderFieldConfig needs to have access to:

   type Error =
       /// <summary>
       /// Used to represents an empty field
       /// </summary>
       | RequiredFieldIsEmpty
       /// <summary>
       /// Used to represents an error due a validation failed like when parsing a field value.
       /// </summary>
       | ValidationFailed of string
       /// <summary>
       /// Used to represents an external error
       /// <para>For example, it is used when doing server side validation</para>
       /// </summary>
       | External of string

  And the list goes on. I think for now, this is not worth it looking into it. This could be revisited once Fable is able to consume pre-compiled packages from NPM for example.

  Or we expose the require API via a global module for usage in TypeScript code. I will left that to explore for others