[FEAT] Detect Complex Gateway

[csouchet]

Is your feature request related to a problem? Please describe.
Given a bpmn input source, detect the BPMN Complex Gateway.

Note for implementation
See the development documentation for details.

Some tasks that are part of the implementation

• Some guidelines are proposed in ShapeBpmnElementKind
• Do not forget to add or update related tests
• The initial rendering should be added in gateway-shapes.ts

Additional context
The final shape rendering of the Complex Gateway won't be done as part of this issue and will be managed later in #794

⚠️ Check the contribution guidelines for BPMN support