Icon for collapsed event subprocess

[rajgoel]

Is your feature request related to a problem? Please describe.

Currently, there is only an icon for expanded event subprocesses, but not for collapsed ones.

Describe the solution you'd like

It would be nice to have an icon for collapsed event subprocesses, i.e. analogously to the icon for collapsed subprocesses (with the + marker).

Describe alternatives you've considered

Continue using the icon for expanded event subprocesses, but this is inconsistent with the icons used in the replace popup menu for other elements.

Additional context

This repo provides a module to collapse/expand event subprocesses from the replace popup menu: https://github.com/bpmn-os/bpmn-js-collapse-event-subprocess/

[nikku]

Makes sense. We're happy to incorporate one if you contribute it. Moving to backlog.