Builds the layer for one hierarchy series.
The walk is the caller's rather than this function's, because the count check wants its length before the layer is built and walking twice doubles every allocation and every getValue() the walk makes -- see hierarchyNodes.
getValue()
The series to read
Its nodes, as hierarchyNodes walked them
One selector per node in walk order, when the series is one whose marks can be paired with it
The layer, or undefined when the series carries no nodes
undefined
Builds the layer for one hierarchy series.
The walk is the caller's rather than this function's, because the count check wants its length before the layer is built and walking twice doubles every allocation and every
getValue()the walk makes -- see hierarchyNodes.