[11.x] fix the method explodeExplicitRule to support Customizable Date Validation

[mrvipchien]

The Date Validation returns a string date|date_format:Y-m-d so that when a Form Request using it such as:

return [
    'from' => ['required', Rule::date()->after('today')]
]

we'll get the error: Method Illuminate\Validation\Validator::validateDate|dateFormat does not exist