Embed layli file features in output SVG

**A summary of what you would like to see added.**

See here for details of `data-*` attributes that could be used for this:

* [https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/data-*](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/data-*)
* https://developer.mozilla.org/en-US/docs/Learn/HTML/Howto/Use_data_attributes

Maybe we could add the relative order of the nodes and paths as a custom attribute.

**User Stories**
Any user stories that make clear what you would like added. Plese keep them relevant to the feature that would like added - you can always raise another feature request if they dont.

_As a_ someone
_I want_ somethis specific
_So that_ I can achieve some outcome

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.