Trace types that share the hierarchy extraction: one node per mark, named by
the path from the root down to it.
A treemap lays the tree out as nested rectangles, a sunburst as concentric
arcs and an icicle as depth-ordered bands; the tree is the same, so all three
are built by buildTreemapLayer and differ only in the type the layer
announces — which is what makes the sunburst pan by the node's angle around
the dial.
Trace types that share the hierarchy extraction: one node per mark, named by the path from the root down to it.
A treemap lays the tree out as nested rectangles, a sunburst as concentric arcs and an icicle as depth-ordered bands; the tree is the same, so all three are built by buildTreemapLayer and differ only in the type the layer announces — which is what makes the sunburst pan by the node's angle around the dial.