Option to hide unused sequence diagram participants

[securitygeneration]

Describe the solution you'd like
When creating sequence diagrams, I commonly re-use my entire participant list, so that I can easily reference any actor in my solution as-and-when needed for this particular sequence flow. Mermaid, however, displays all participants, irrespective of whether they were actually used in the flow, meaning I have to go and manually remove the superfluous participants.

I would like to see an option that says "hideUnusedParticipants". In my mind this should probably even be the default, as there are few scenarios where you'd want to display an unused participant.