Allow control of the doughnut chart radius

[etimberg]

Adds a new option, radiusPercentage that shrinks the outside radius of doughnut / pie charts. A percentage is used to enable more flexibility during responsive conditions.

Closes: #3923

[benmccann]

Maybe this should be called padding to be more generic and so it could eventually be made available to all chart types?

[kurkle]

I'm not sure I get the use case. layout.padding could be used, but I don't think that supports percentages.
If planning on having mutiple pies in one canvas, we should debate if having a chartArea per dataset and handling that in layout would be better?

[etimberg]

I don't think multiple pies per canvas is something I'd want to do. It seems like it'd be a lot more complex for a few small use cases.

I could make this into a padding option. It'd be inside the chart area only. From the original issue, it was unclear if users wanted pixels or percentages. I went with a percentage to match the cutoutPercentage that already exists for pie/doughnut charts

[benmccann]

I think if we made this a padding option it'd be fine to support percentages. Ideally we'd support percentages and pixels, but that wouldn't have to be done immediately

[benmccann]

This looks fine to me other than maybe the option name. What did you guys think about it?

[kurkle]

I too dislike having 'percentage' in the option name. Both options should be changed to be consistent through. One option would be to use only cutout and radius, requiring string with % for percentage and assume number are pixels. But I think that is out of the scope of this PR.

[benmccann]

Yeah, keeping "percentage" out of the name is a good point too. My main thought was to call it padding so that the same name could at some point be used for other chart types

[kurkle]

This looks fine to me other than maybe the option name. What did you guys think about it?

The name is consistent with other options currently, so if we want to change those then its can be done in another PR. This should be merged, IMO.

[benmccann]

I don't have strong feeling about it. If you'd like to merge that's okay with me. It will need to be rebased though

[etimberg]

Going to close this. I'm sure there's a better way to achieve this