[FEATURE]: Add a polar heatmap

[bpwrs]

Description

Recommend adding a polar heat map plotting option. Essentially the polar scatter plot but include heat map bins instead of the points.

Why should this feature be added?

Polar heatmapping is extremely useful when looking at statistics/distributions in scenarios where the statistically meaningful bin limits do not map neatly onto a cartesian grid.

[camdecoster]

Thanks for the idea! I'm going to transfer this issue to plotly.js, because that's where it would need to be added first.

Could you please provide some examples of type of chart? We're always interested in new traces, but we don't always have time to add them. Would you be interested in adding this feature to the library?

@alexcjohnson has this type of trace been discussed before?