Add connected fields support to the Twill 3 form builder

[joyceverheije]

Description

This has been reported many times on Discord as missing from the new form builder. Developers were forced to use a BladePartial field to use the @formConnectedField directive or component in a Blade file.

Now they can simply use ->connectedTo($fieldName, $fieldValues) on a form builder field to use this functionality. Additional options are supported by a third parameter of type array.

Examples

Checkbox::make()->name('use_source_description'),
Wysiwyg::make()
    ->name('source_description')
    ->connectedTo('use_source_description', true),
Wysiwyg::make()
    ->name('description')
    ->connectedTo('use_source_description', false),

Checkbox::make()->name('use_source_description'),
Wysiwyg::make()
    ->name('source_description')
    ->connectedTo('use_source_description', true, ['keepAlive' => true]),
Wysiwyg::make()
    ->name('description')
    ->connectedTo('use_source_description', false, ['keepAlive' => true]),

[Jigsaw5279]

I've literally JUST been trying to find how to do this when the notification about this PR came in..

[Tofandel]

There is one thing that's not possible with the connectedTo approach that is possible with blade and that is nested connectedTo for multiple dependencies

[ifox]

@Tofandel good point, could you share a Blade example?

[Tofandel]

Eg an input that shows if 2 fields have a specific value

<x-twill::formConnectedFields
    field-name="type"
    field-values="video"
>
  <x-twill::formConnectedFields
      field-name="provider"
      field-values="youtube"
  >
      <x-twill::input
          name="video_embed"
          label="Video embed"
      />
  </x-twill::formConnectedFields>
</x-twill::formConnectedFields>