Interactive matplotlib charts

### What is the problem or limitation you are having?

It would be great to have intractability within a toga_chart.Chart() object. I understand Chart() is calling matplotlib. Does that mean any matplotlib styling/functionality can be used within a Chart() object? Currently, a Chart() is plotted as a static thing. I'd like to enable the standard matplotlib controls (pan, zoom, save) and also add a DraggableLine element. Is intractability currently possible, or will this feature be added?

### Describe the solution you'd like

If this is not already possible given Chart() is using matplotlib, I would love to see this added as a feature and/or have someway to call any matplotlib stuff (e.g., pyplot.ion).

### Describe alternatives you've considered

I tried just calling `pyplot.ion`, but that does not enable intractability.

### Additional context

_No response_

Start with the toga_chart.Chart entry point and inspect how it uses matplotlib and pyplot. Determine whether pan, zoom, save, and a DraggableLine can be supported, then define completion as interactive chart controls working within Chart rather than only static plotting.

Written by the indexing model from the issue text.