feat: add plot/vega/mark/symbol/encoding-set

[Sachinn-64]

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• feat: add plot/vega/mark/symbol/encoding-set

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@stdlib-js/reviewers

[gururaj1512]

@Sachinn-64, the docs mention that the default value for the angle properties is 0, while the default value for shape is 'circle'. We need to define these defaults in defaults.js and map the corresponding properties to their default values in the constructor.

[kgryte]

the docs mention that the default value for the angle properties is 0, while the default value for shape is 'circle'. We need to define these defaults in defaults.js and map the corresponding properties to their default values in the constructor.

@gururaj1512 I thought about this some more. And actually, we cannot set defaults in encoding sets.

We cannot set a default because an encoding set is contextual and needs to be bound to a property set. Those sets are enter, update, exit, and hover. We don't know a priori where the "default" should be set.

E.g., for a line chart, I might have enter, update, and exit encoding sets. Which one should interpolate be the default setting? All of them? Likely not, as this would be redundant. Instead, for encoding sets, we have to defer to Vega, as we don't know how the encoding set will be consumed.

[kgryte]

LGTM

[kgryte]

As the CI failure is expected, I'll go ahead and merge.