mapChildren method
Updates the content of each child with the value returned by mapper
Implementation
Stream<Snapshot> mapChildren(
dynamic Function(String key, Snapshot value) mapper) =>
map((s) {
var keys = s.asMap()?.keys;
if (keys == null) return s;
return keys.fold(s, (s, k) => s.setPath(k, mapper(k, s.child(k))));
});