[DOC] Display BPMN diagrams in a div with fixed size

[tbouffard]

⚠️ IMPORTANT NOTE ⚠️ : what is described here may be a more general issue: it probably impact all integration of bpmnVisualization. If confirmed, create a dedicated issue.

Currently, the bpmn-container HTML element doesn't used a fixed size, so the container size changes on panning or zooming.

The following video shows what happens in reference/display.html.

bpmn-container_expanded_with_mouse_navigation.mp4