replaceByKey function
Replaces the node with key with replacement.
Returns false if key matches the root node or is not found.
replaceByKey(root, 'Text_old', UI.text('New'));
Implementation
bool replaceByKey(FFNode root, String key, FFNode replacement) {
final result = findParentByKey(root, key);
if (result == null) return false;
replaceChild(result.parent, result.child, replacement);
return true;
}