add support for enumerate(Array, Column)

[guilhermeleobas]

Fix #420

Heavily inspired in the iternext code for tuples:
https://github.com/numba/numba/blob/61ec1fd0f69aeadece218dccf4c39ebc5c7dfbc4/numba/cpython/tupleobj.py#L159-L187

[pearu]

I have a question and remark about ordering of rows in select.

[pearu]

What is the issue with ColumnList case?

[pearu]

The row order of select is undefined and to ensure correct order (that enumerate needs), one should use

select rowid, i4 from {omnisci.table_name} order by rowid;

[guilhermeleobas]

Done! Can you check if what I did is what you meant?

[pearu]

Yes. Now the expected_result ought to be uniquely defined. The query

select * from table(col_enumerate(cursor(select i4 from {omnisci.table_name})))

is vulnerable to the same effect but it could be that table functions results are always ordered. If not, at some point we should see this test breaking, until then, let's leave it as it is.

[guilhermeleobas]

Supporting enumerate(ColumnList) will require a bit more of work, and I'll do it in a later PR.

[pearu]

I have a nit to remove dead code from tests, otherwise LGTM, thanks, @guilhermeleobas !

[pearu]

LGMT! Thanks, @guilhermeleobas !