Sparse array iterators include index position.

Sparse array iterators include index position.

Iterators over the sparse array structures have gained an initial argument
which indicates the index into the array of the element.  This can be used,
e.g., to delete or modify the associated value.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8229)