Add optional callback for ArrayValidator.

[timkelty]

This may be a stretch, as I'm not sure there is an immediate use for it, but I found it helpful authoring a plugin.

If not, at least I can extend ArrayValidator and add it now that #4309 is fixed.

Example usage (validating an attribute is an array of MyModels):

    public function rules()
    {
        return [
            ['myModels', ArrayValidator::class, 'callback' => function ($value) {
                return $value instanceof MyModel;
            }],
        ];
    }

[brandonkelly]

Hm yeah I don’t think there’s any precedence for this. You could always just check for errors on the model attribute after validate and do whatever you need to do with them from there, or write your own validation method.

[timkelty]

Yep, sounds good 🤠.