[SwitchInput] Support for configurable "onSwitchChange" handler

[Wirone]

When I want to hook into SwithInput and use onSwitchChange plugin option:

DetailView::widget([
    'id' => 'my-switch-input',
    'model' => $model,
    'enableEditMode' => true,
    'mode' => DetailView::MODE_EDIT,
    'attributes' => [
        [
            'attribute' => 'myFlag',
            'type' => DetailView::INPUT_SWITCH,
            'pluginOptions' => [
                'onSwitchChange' => 'function () { console.log("I AM SWITCHING!"); }'
            ],
            'format' => 'raw',
            'value' => $model->myFlag,
        ],
    ],
])

I got TypeError: _this.options.onSwitchChange.apply is not a function.

Function configured in widget's pluginOptions is not passed to JS as function, but as string:

window.bootstrapSwitch_bad7d579 = {"onSwitchChange":"function () { console.log(\u0027I AM SWITCHING!\u0027); }"};

I need it to display confirmation box just before changing input's state.

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[Wirone]

As far as I see this is only used in switchChange.bootstrapSwitch event handler to return to previous state if custom handler returns false. I can use it for my needs too, but as a side note it would be good to introduce beforeSwitchChange.bootstrapSwitch event and if handler returns false do not change the state (so switchChange.bootstrapSwitch wouldn't be triggered).