Provide test checking canvas is visible when editing source code and getting back to a valid state

[apupier]

In some cases, Kaoto is unable to render a diagram on the canvas (even if in the future it will be more and more resilient), when it is happening, we should ensure that the diagram is shown again when the user is modifying the source code and getting back to a valid state.

related to KaotoIO/kaoto#714