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

As a user I want to copy and paste parts of my diagram between different browser/app windows.

Use case: Have multiple diagrams opened in different tabs, but also have diagrams opened in different bpmn-js based applications (Camunda Modeler, Camunda Web Modeler, bpmn.io demo).

Describe the solution you'd like

• If I copy parts of the diagram it is put into the system clipboard in a way that
• Pasting with the canvas selected pastes from the system clipboard, if it holds bpmn-js contents

Describe alternatives you've considered

None.

Additional context

The web platform provides clipboard API as well as copy events we may be able to hook into.

On the bpmn-js side we'd need to ensure our copy/paste implementation is side-effect free, and the copied tree is serializable.

Depends on bpmn-io/diagram-js#659.