Aggregate + non-aggregate expressions can be mixed in places where they should not be allowed to

[sgrif]

We only enforce that you cannot mix aggregate/non-aggregate expressions inside of tuples, but this needs to be done everywhere. Examples of queries which are currently accepted but should not be:

foo.select(nullable_int_col + max(nullable_int_col));
sql_function!(f, F, (x: Nullable<Integer>, y: Nullable<Integer>) -> Nullable<Integer>);
foo.select(f(nullable_int_col, max(nullable_int_col));

I suspect we won't be able to fix this without reworking aggregates in a way that enables group_by support, meaning it will require a major breaking change.