Make the `chart.data.datasets.dataset.hidden` reflect the actual value

### Feature Proposal

```js
chart.data.datasets = Object.keys(data[territorialUnit]).map(representationMethod => {
const hidden = chart.data.datasets.find(entry => entry.label === representationMethod)?.hidden;

return {
label: representationMethod,
data: Object.fromEntries(Object.entries(data[territorialUnit][representationMethod]).filter(filter)),
borderWidth: 1,
hidden: hidden ?? representationMethod !== defaultRepresentationMethod,
};
});

chart.update();
```

The above is always resetting `hidden` to the default value (the `!==`), because `dataset.hidden` is not updated when user interacts.

I'm assigning datasets this way instead of `.data =` because I'm downloading the data asynchronously, so there's no initial data when the chart is created. I'm not checking if the dataset already exists, because in my opinion this would be unnecessary code.

### Possible Implementation

_No response_