insert method
Implementation
void insert(int index, [Map<String, dynamic>? value]) {
final count = _ids.length;
_registerSlot(count, null);
for (var slot = count - 1; slot >= index; slot--) {
_writeSlot(slot + 1, _readSlot(slot));
}
_writeSlot(index, value ?? {});
_ids.insert(index, _newId());
_form.finalizeArray(name);
}