RFC: Integrating rsvg-rs into librsvg

It would be nice to integrate rsvg-rs into librsvg for various reasons:

• rsvg-bench lives outside of librsvg, and that's weird. But since it depends on rsvg-rs, it must remain an external tool for now.
• rsvg-dimensions has been ported to Rust; it has the same issue.
• It would be nice to port librsvg's utilities (rsvg-convert, rsvg-view-3) to Rust.
• It would be nice to have our testing infrastructure done in Rust.

I'd like to open this as a brainstorming issue to see the implications of merging the rsvg-rs repository into librsvg.