Materialize: rename and reorder columns

[erezsh]

No description provided.

[leoebfolsom]

@erezsh does this also address not only the ordering, but also the point that I raised in Slack that

column names alternately use a/b and 1/2 to represent the left and right tables

Will they all now materialize as a/b instead of 1/2?

Edit reread the code and I think you've covered it--thanks!

[erezsh]

@leoebfolsom Let me know if it behaves as you'd expect, so I can merge it in.

[leoebfolsom]

This works as expected--thank you! @erezsh

[leoebfolsom]

@erezsh please merge when you're ready.