[Idea] Illustration centering on anchor

[asl97]

I had this idea of allowing an anchor to be passed to the Illustration's centered instead of just true.

I have a Proof of concept working on canvas but bugged on SVG.

The SVG version doesn't seem to like to get rendered multiple times, any previously rendered seem to get removed when rendering to a different Illustration instance.

Maybe you can figure it out.

Demo https://asl97.github.io/zdog/demos/centered/

Poc, bugged on svg, patch change: main...asl97:zdog:main

[asl97]

Turns out each shape stores and reuse it's own SVG elements, probably for performance, browser limitation of not being able to have same element at multiple location.

Worked around the issue using this.element.innerHTML = this.element.innerHTML to basically make the SVGs elements be a copy.

I think it's good enough so I will make a pull request.