Graphviz/DOT language support

[ctem]

Thanks for this great plugin! While the Diagrams as Code plugin supports Graphviz and many other diagram libraries by relying on Kroki, I appreciate Fenced code plus's library vendoring approach as a lighter-weight offline alternative to managing a local Kroki instance.

Some libraries to consider:

• TS: ts-graphviz
• JS: d3-graphviz, Viz.js

(Note that the desire to implement DOT in Mermaid has gone unaddressed for roughly a decade.)