clear method Null safety
Remove all elements from this linked list.
Implementation
void clear() {
_modificationCount++;
if (isEmpty) return;
E next = _first!;
do {
E entry = next;
next = entry._next!;
entry._next = entry._previous = entry._list = null;
} while (!identical(next, _first));
_first = null;
_length = 0;
}