Add elements.arc.angle in documentation

[mp3000mp]

Using elements.arc.angle option can be a workaround for #4751 and make #6472 useless.

Demo here : https://jsfiddle.net/h1e78vbq/

[benmccann]

what does "for polar only" mean? That the option is available only for the polar chart or that default is circumference / (arc count) only for the polar chart? If the latter, what is the default for other chart types?

[mp3000mp]

We have two types of chart using elements.arc :

• Polar area
• Pie/Doughnut

I tried to set elements.arc.angleoption in Pie/Doughnut chart. It doesn't override the natural angles computation.

So it seems that this option is available only for polar chart, and I think it's a good thing.

[benmccann]

Ok. I think it might be clearer to put "for polar only" next to the option name rather than the default value. How about:

angle (polar area chart only)

[kurkle]

Rather than stating its for polar only, why not move it to

Chart.js/docs/charts/polar.md

Lines 58 to 68 in f68b8ad

	### Styling
	The style of each arc can be controlled with the following properties:
	| Name | Description
	| ---- | ----
	| `backgroundColor` | arc background color.
	| `borderColor` | arc border color.
	| `borderWidth` | arc border width (in pixels).
	All these values, if `undefined`, fallback to the associated [`elements.arc.*`](../configuration/elements.md#arc-configuration) options.

Like weight in pie/doughnut