Stunner - Zoom widget duplicated after `setContent` calls

With the release of Kogito Tooling Chrome Extension, we could see this behaviour with more clarity. When switching between "Original" and "Changes" diagram on a PR with supported file formats (.dmn and .bpmn), we can see that the Zoom widget on the bottom-right corner gets darker and darker after each switch.

Inspecting the DOM we can see that multiple `Zoom widgets` are being created.

This behaviour can also be seen on the VSCode extension, where if you open a BPMN/DMN file, you'll see a duplicated Zoom widget. One of them does nothing and the other one controls the zoom properly. The reason why this happens is that when we open a file being on VSCode or the Chrome Extension, we first call an empty `setContent` and then we pass the actual file content that we want to open.