feat: ergonomic way to use aggregates as window functions

[Michael-J-Ward]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

@timsaucer commented

I think another thing that would be very helpful would be to have a more ergonomic way to use aggregates as window functions. I could see two ways

• Update functions.window to take an aggregate function instead of a registered function name.
• Add something like Expr.over() so you could do something like first_value(col("a")).over(window) where window is a window frame definition.