[FEAT] Display Embedded Sub-Process (Sub-Process)

[csouchet]

Is your feature request related to a problem? Please describe.
Given a bpmn input source, display the bpmn Sub-Process.

A Sub-Process is an Activity whose internal details have been modeled using Activities, Gateways, Events, and Sequence Flows.

To know if a Sub-Process is expanded or not, use isExpanded attribute of BPMNShape.

Describe the solution you'd like
Manage all Sub-Processes declared in the bpmn input source

Describe alternatives you've considered
N/A

Additional context
The final shape rendering of the Sub-Process won't be done as part of this issue and will be managed later