unloadSubtree function
Detaches a loaded lazy subtree node's content; it can be loaded again with
loadSubtree. No-op if node is not a lazy placeholder.
Implementation
void unloadSubtree(Node node) {
if (lazyInstanceOf(node) == null) {
debugPrint(
'fscene: unloadSubtree on a node that is not a lazy placeholder',
);
return;
}
node.removeAll();
}