fix(shape): conditionally render Arc without data

[williaster]

🐛 Bug Fix

This supersedes #892 and partially addresses #886, it

• conditionally renders @visx/shapes Arc when no data is specified if angles + radii are specified
• adds a warning if we render null due to missing data + angles + radii for better dev experience

As mentioned in both issues above, d3-shape supports two types of usage for arc(), it can be configured with constant angles + radii, or passed them (as data in @visx/shape):

const arc1 = d3.arc();
arc1({ innerRadius, ... }); // "M0,-100A100,100,0,0,1,100,0L0,0Z"

const arc2 = d3.arc().innerRadius(...)...;
arc2(); // "M0,-100A100,100,0,0,1,100,0L0,0Z"

@hshoff @kristw
cc @oscar-broman @thecodeah

[coveralls]

Pull Request Test Coverage Report for Build 371119529

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 60.879%

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Totals
Change from base Build 368243629:	0.07%
Covered Lines:	1632
Relevant Lines:	2535

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💛 - Coveralls

[williaster]

got a fresh laptop and this was changed