Add data-selected binding

It will enable `data-selected` bindings.

```js
values = [
  {value: 0, label: "Test 1", selected: false},
  {value: 1, label: "Test 2", selected: true},
  {value: 2, label: "Test 3", selected: false},
]
```
```html
<select>
  <option each="values" value="{value}" data-selected="selected">{label}</option>
</select>
```