replace method
Replaces the first occurrence of value in this list.
Runtime is O(n).
Implementation
bool replace(T existing, T replacement) {
final index = _rawList.indexOf(existing);
if (index == -1) return false;
_rawList = _rawList.toList();
_rawList.removeAt(index);
_rawList.insert(index, replacement);
_listChanged();
return true;
}