[FEA] Support multiple sources/destinations for gather and scatter

Currently, we have the `gather` and `scatter` APIs that perform on a single source table. Sometimes, we may want to operate on multiple sources/destinations so it would be great if we can support that. In such cases, the input iterators into these APIs would be a zip iterator or a pair of iterators pointing to `{column_index, row_index}` of the source/destination tables (https://github.com/rapidsai/cudf/pull/9130#discussion_r701405591).