Now, I'm pretty sure that the last time we touched pull_var_clause's
> API, we intentionally set it up to force every call site to be visited
> when new behaviors were added. But right at the moment that's looking
> like it was a bad call.
>
> An alternative API design could look like
>
> #define
Over in the "Optimizer questions" thread, it's become apparent that
we need to fix pull_var_clause() to offer multiple behaviors for
WindowFunc nodes that are parallel to the ones it has for Aggrefs
(viz, reject, recurse, or include in result). This should've been
done when window functions were
