iframe being rendered strangely in the canvas view

Hello,

The issue described below can be reproduced on the official demo at https://grapesjs.com/demo.html

When I try to add an iframe in a custom code block, the view tends to replace the iframe by a div, which breaks the layout of the iframe. However, the model seems to have the correct iframe since it is shown correctly in the `view code` modal, or by using `editor.getHtml()`.

For example, if I add this iframe which is an embed YouTube video:
```html

```

This is what the canvas view will use, parts of the iframe attributes are now on a parent div:
```html