Iterates over children in a shape.

Iterator supports two usage scenario:

iteration over direct children;
iteration over shapes of a specified type.

To retrieve direct children of a shape, ShapeIterator should be used as follows:

const face = ...;
for (let child of new ShapeIterator (face)) {
  const type = child.type;
}

To retrieve children of a particular type, ShapeIterator should be used by specifying a type of interest as follows:

const solid = ...;
for (let child of new ShapeIterator (solid, ShapeType.FACE)) {
  // "child" has Face type
}

When using the latter approach exploration is done traversing the graph of subshapes in a depth-first manner. Each subshape will be found as many times as it is registered in the parent subshape. For instance, a seam-edge will be encountered twice, with forward and reversed orientations.

The order of returned subshapes is deterministic and corresponds to the order in which the subshapes were added during construction.