Date diff with `-` operator

[max-sixty]

From @matsonj: https://twitter.com/matsonj/status/1537969665070092295

Currently we don't handle this, but I think we could without that much trouble:

derive x = @2022-01-01 - @2021-01-01

SELECT
  DATE '2022-01-01' - DATE '2021-01-01' AS x

...should be DATEDIFF(DATE '2022-01-01', DATE '2021-01-01')

[aljazerzen]

Great point, i agree

This should be implemented more generally via "operator overloading" aka some way of declaring what to do when a binary (or even unary) operation is applied to two arbitrary types:

maybe something like:

operation - a<date> b<date> -> s"DATEDIFF(DATE ${a}, DATE ${b})"