seperatedIndexed method
Implementation
List<E> seperatedIndexed(E Function(int index) separator) {
final newList = <E>[];
for (var i = 0; i < length; i++) {
if (i == 0) {
newList.add(this[i]);
} else {
newList.add(separator(i));
newList.add(this[i]);
}
}
return newList;
}