pruneEmptyContainers function
Cleans node from the document if it's an empty InlineContainerNode.
Climbs the tree and repeats if necessary (ex pruneEmpty).
Implementation
void pruneEmptyContainers(FNode node, Root root) {
if (node is! InlineContainerNode) return;
final children = (node as InlineContainerNode).getChildren();
if (children.isNotEmpty) return;
final parent = findParent(root, node);
if (parent == null) return;
removeNode(root, node);
if (parent is InlineContainerNode) pruneEmptyContainers(parent, root);
}