fix(laravel): validate the model instead of body

[soyuka]

Q	A
Branch?	4.1
Tickets	fixes #6932
License	MIT

With Eloquent, the model properties are in snake_case.
We've configured Symfony to convert camelCase to snake_case during normalization, so users send payloads like this:

{"surName": "foo"}

However, the serializer, if you send it:

{"sur_name": "foo"}

The serializer will correctly skip this property, but the HTTP Body has the field that appears to be correct.

But this causes problems with API Platform and Laravel. For instance, if we set a validation rule like this:

#[ApiResource(
    operations: [
        new Post(
            uriTemplate: '/issue_6932',
            rules: [
                'sur_name' => 'required'
            ]
        )
    ],
)]
class Issue6932 extends Model
{
}

The request will pass validation, but it won't pass serialization, and thus it will break during database insertion (for example, with non-nullable fields).
The issue with #6932 is that as Laravel validator works on arrays, we used the HTTP Body to validate. Except that the serialization phase of API Platform should already strip some unwanted attributes.

To resolve this we moved the ValidateProvider to work on the deserialized body. With eloquent models we can use $model->toArray() but for non-eloquent models we need to use the ObjectNormalizer again.

In this PR we also added a name conversion on validation property paths.