Support transform of element with `transform-box: fill-box; transform-origin: 50% 50%`

Each of these SVG's defines a centred square:

```svg

```

Suppose we `loadImage` the SVG then `drawImage`, and finally save as PNG.
- The first two work as expected.
- However _the third produces an empty PNG_.

Code loading an SVG and saving as PNG.

```ts
import fs from 'fs';
import { promises as stream } from 'stream';
import nodeCanvas from 'canvas';

const svgPath = '/path/to/file.svg';
const image = await nodeCanvas.loadImage(svgPath);

const canvas = new nodeCanvas.Canvas(image.width, image.height);
canvas.getContext('2d').drawImage(image, 0, 0);

const outputSvgFilePath = '/path/to/file.png';
await stream.pipeline(
canvas.createPNGStream({}),
fs.createWriteStream(outputSvgFilePath),
);
```

This problem arises naturally in the context of [BoxySVG](https://boxy-svg.com/app).
I just created a centred square, then rotated it by 90° using the Geometry panel.