Fix ARIA violation: add innerElementRole property

[jussirantala]

innerElementRole property added for the user to be able to set role. Without this it is not possible to pass ARIA violation checks. For example you could set innerElementRole to "rowgroup" and role for each list item to "row" and the screen reader would understand that this is list.

[Terence-Cheng]

I also had this problem, but I solve it with innerElementType like below.

        <List
            innerElementType={(innerProps) => (
                <div
                    {...innerProps}
                    role="rowgroup"
                />
            )}

      ....