Pixi: for transformed doucments check that all amp-element layouts are ssr'd

We should show an error for the following doc:

```

 
```

as the amp-ad is missing:

```
class="i-amphtml-layout-fixed i-amphtml-layout-size-defined"
```

I think checking if each AMP element with a layout contains `layout="$LAYOUT" class="i-amphtml-layout-$LAYOUT`.