Summary

close #104

This PR introduces a LineAnnotation spec so the user can specify what annotations on a chart they want.

Since this is the first of the Annotation features, this also introduces a bit of scaffolding for the annotations overall. This implementation allows a user to define a set of annotations by defining one of three specs (LineAnnotation, RectangleAnnotation, and TextAnnotation).

Within a LineAnnotation spec a user may define:

  /** The id of the annotation */
  annotationId: AnnotationId;
  /** Annotation type: line, rectangle, text */
  annotationType: AnnotationType;
  /** The ID of the axis group, generated via getGroupId method */
  groupId: GroupId; // defaults to __global__; needed for yDomain position
  /** Annotation domain type: XDomain or YDomain */
  domainType: AnnotationDomainType;
  /** Data values defined with value, details, and header */
  dataValues: AnnotationDatum[];
  /** Custom line styles */
  lineStyle?: Partial<AnnotationLineStyle>;
  /** Custom marker */
  marker?: JSX.Element;

dataValues are defined in terms of data relevant to a scale within the chart. If the domainType is xDomain, then the annotation points will be scaled relative to the xDomain scale. If the domainType is yDomain, then the annotation points will be scaled relative to a yDomain scale; we get the relevant scale by lookup up against this.yScales with the groupId defined on the spec.

Checklist

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• This was checked for cross-browser compatibility, including a check against IE11
• Proper documentation or storybook story was added for features that require explanation or tutorials
• Unit tests were updated or added to match the most common scenarios
• Each commit follows the convention