Provide an intuitive way to get a Series and/or array out of an index object

[kellyjoy15]

I haven't spent a great deal of time thinking about it, but the following are all things I would intuitively think to try:

ak.Series(index_obj) --> <ak.Series> ak.array(index_obj) --> pdarray / categorical / strings .. based on the relevant dtype index_obj.values --> same as above