Automaticaly add enctype to the form

[aadutskevich]

The same issue as it was with standart yii2 fileInput yiisoft/yii2#8779

[kartik-v]

Will not work here the way the code is written - because this class is not an instance of yii\widgets\ActiveField unlike the yii fileinput which is an activefield instance.

This FileInput widget here can be used with and without a form and via ajax as well... so it makes sense for users to set the enctype property to the form based on their own need (as it is not mandatory for the other cases like ajax).

[aadutskevich]

Ok, let we add an instance check, So if we use widget with ActiveField then the form enctype option will be created.

    `if ($this->field instanceof \yii\widgets\ActiveField && !isset($this->field->form->options['enctype'])) {
	    $this->field->form->options['enctype'] = 'multipart/form-data';
    }`

[kartik-v]

Ok -- this above code will work for InputWidget... will figure out and include this...