Implement resvg renderer

[kklemon]

See RazrFalcon/resvg and the unofficial Python binding baseplate-admin/resvg-py.

They claim to offer an even more complete and correct implementation of SVG than, for instance, Chrome. In my tests, the results generally look very good. However, they are two major shortcomings:

• The library is incredibly slow, probably due to lack of GPU support. Around 20 seconds to render a full Penpot page of medium complexity, e.g. Plants App.
• Apparently no support for cross-links. This can be fixed relatively easily by inlining all asset urls.

I would still implement it as an alternative to the headless Chrome-based renderer as the latter works by taking a screenshot which is a bit hacky and does not support transparency.