[Sequence] Improve group position (Move the unaffected participant aside)

Context

To follow:

• https://forum.plantuml.net/7710/teoz-and-%26-within-groups-is-not-working?show=7756#c7756

Wanted feature

• Could you improve group position (Move the unaffected participant aside)?

Examples

Correct example ✔️

@startuml
x -> x: start
group test
a -> b: 1
b -> c: 2
end
d -> d: next
@enduml

Not working example :x: (Participant d should be outside the group as on the correct example)

@startuml
x -> x: start
group test
a -> b: 1
c -> c: 2
end
d -> d: next
@enduml

Regards, Th.