Add more specs to verify current implementation

[philippfromme]

Proposed Changes

Added

Collaborations

Only the first participant's process is laid out.

Associations

Associations are not laid out.

Event sub-processes

Event sub-processes are laid out.

Text annotations

Text annotations are not laid out.

Checklist

To ensure you provided everything we need to look at your PR:

• [x] Brief textual description of the changes present
• [x] Visual demo attached
• [ ] Steps to try out present, i.e. using the @bpmn-io/sr tool
• [ ] Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}