feat!: make $rename()'s behavior closer to python polars'

[eitsupi]

A follow up for #1122

• old_name = "new_name" instead of new_name = "old_name"
• Allow a function input

[eitsupi]

@etiennebacher This will definitely break tidypolars, but hopefully it is a meaningful change in terms of consistency with Python.

[etiennebacher]

Nice, I prefer this order and actually I originally put this old = new order when I implemented it one year ago but we decided to follow dplyr for more consistency (#239).

This will definitely break tidypolars

Not a big deal, I'll just need to update the internals but it won't change the external behaviour.

Also for those who use polars directly, this will clearly error and not just fail silently.

[eitsupi]

Nice, I prefer this order and actually I originally put this old = new order when I implemented it one year ago but we decided to follow dplyr for more consistency (#239).

Hmmm, I completely forgot about this.
And I always have trouble with the order of dplyr::rename() as well (although new=old makes more sense since it is consistent with dplyr::select())