Add support for Mindmap (Mermaid)

[Pyroseza]

Add support for Mindmap (Mermaid)

See https://mermaid.js.org/syntax/mindmap.html

Available since 9.2.0

Example from docs

mindmap
  root((mindmap))
    Origins
      Long history
      ::icon(fa fa-book)
      Popularisation
        British popular psychology author Tony Buzan
    Research
      On effectiveness<br/>and features
      On Automatic creation
        Uses
            Creative techniques
            Strategic planning
            Argument mapping
    Tools
      Pen and paper
      Mermaid

Current error as seen in Joplin