insert method
Inserts the object at position index
in this list and returns a new immutable list.
This increases the length of the list by one and shifts all objects at or after the index towards the end of the list.
The list must be growable.
The index
value must be non-negative and no greater than length.
Implementation
@useCopy
IList<T> insert(int index, T element) {
// TODO: Still need to implement efficiently.
return IList._unsafeFromList(toList(growable: true)..insert(index, element), config: config);
}