[feature] show music rendered by the ABC plugin inline

[barnabywalters]

Currently, musical notation rendered by the joplin ABC plugin isn’t shown inline in the rich markdown view. Not sure what it would take for this to work out (presumably modifications to both plugins?) but it would be a great feature to have if technically possible!

I might be up for helping out getting it working if someone who knows how the joplin-specific parts work can give me an overview of what would need to be changed and where.