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

Reproduce the iframe behavior in the official demo using a custom code block, then compare the canvas view with the view code modal and editor.getHtml(). Trace where the canvas replaces the iframe with a div and moves its attributes; done means the canvas preserves the iframe layout and remains consistent with the model output.

由索引模型根据 Issue 内容生成。