Inconsistency in placement of overflow button when SSR prepends sizer element

In https://github.com/ampproject/amp-wp/pull/5926 I noticed that the `button[overflow]` element was being hidden due to being positioned outside of the parent element:

On non-SSR'ed pages, the preview button appeared at the _top_ inside of the element.

The issue is that on SSR'ed pages, a responsive `amp-iframe` will get:

```html

See more
https://ifpaintingscouldtext.tumblr.com/post/92003045635/grant-wood-american-gothic-1930

```

Whereas on the non-SSR'ed page, this is absent:

```html

See more
https://ifpaintingscouldtext.tumblr.com/post/92003045635/grant-wood-american-gothic-1930

```

The `i-amphtml-sizer` is pushing the computed `top` for the `button` to be the same as the `height` of the sizer, which causes it to move out of view.

We worked around the issue by adding this style rule to consistently place the absolutely-positioned button at the bottom of the container:

```css
button[overflow] {
bottom: 0;
}
```

Nevertheless, I think SSR should consider _appending_ the `i-amphtml-sizer` element rather than _prepending_ in order to ensure consistency when SSR'ed.

Playground examples:

[Without SSR](https://playground.amp.dev/?mode=Pixel+2#share=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) | [With SSR](https://playground.amp.dev/?mode=Pixel+2#share=<!DOCTYPE html>
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/*# sourceURL=/css/ampshared.css*/</style>
  <meta name="viewport" content="width=device-width">
  <link rel="preload" href="https://cdn.ampproject.org/v0.js" as="script">
  <script async src="https://cdn.ampproject.org/v0.js"></script>
  <script async custom-element="amp-iframe" src="https://cdn.ampproject.org/v0/amp-iframe-0.1.js"></script>
  <title>Resizable Iframe w/ SSR</title>
  <link rel="canonical" href="self.html"><style amp-custom>body{padding:20px}</style>
</head>
<body>
  <h1>Resizable Iframe w/ SSR</h1>
  <amp-iframe src="https://embed.tumblr.com/embed/post/2JT2XTaiTxO08wh21dqQrw/92003045635" layout="responsive" width="540" height="280" resizable sandbox="allow-scripts allow-popups allow-same-origin" class="i-amphtml-layout-responsive i-amphtml-layout-size-defined" i-amphtml-layout="responsive">
    <i-amphtml-sizer style="display:block;padding-top:51.8519%"></i-amphtml-sizer> <button overflow>See more</button> <a href="https://ifpaintingscouldtext.tumblr.com/post/92003045635/grant-wood-american-gothic-1930" placeholder>https://ifpaintingscouldtext.tumblr.com/post/92003045635/grant-wood-american-gothic-1930</a>
  </amp-iframe>
  <p> Interesting stuff! </p>
</body>
</html>)
-----------|------------
 | 

Start with the SSR transformation responsible for inserting the i-amphtml-sizer element, using the linked AMP Playground examples and PR #5926 to reproduce the responsive amp-iframe case. Done means the overflow button remains visible and is placed consistently in both SSR and non-SSR output.

Written by the indexing model from the issue text.