protected static Map<String, LeafNode<?>> getAllDescendantLeafNodes(InnerNode node) {
         return getAllDescendantLeafNodes("", node);
     }
Returns a flat map of this node's direct children, including all NodeVectors' elements.
Keys are the node name, including index for vector elements, e.g. 'arr[0]'.
config-lib/src/main/java/com/yahoo/config/InnerNode.java