Cannot configure CRUD field for doctrine entity with json member

[mgiuffrida]

As described in #5680 , the docs recommend mapping json to TextField, TextareaField, or CodeEditorField.

The JSON field should be mapped back to a string, since the Doctrine entity treats it as an array via json_decode().

Even then, using either TextField or TextAreaField fails with a RuntimeException:

The value of the "foo" field of the entity with ID = "1" can't be converted into a string, so it cannot be represented by a TextField or a TextareaField.

  public function configureFields(string $pageName): iterable {
    return [
      ...,
      TextareaField::new('foo')
          ->formatValue(fn ($foo) => json_encode($foo)),
      ...,
  ] 
}

Using CodeEditorField works, thanks to #5759.

To Reproduce EasyAdmin 4.18.0

1. Create a doctrine entity with a json field
2. Create a CrudController as in the example above
3. Try to view the entity in a template, e.g. a crud dashboard