Convert Option<Vec<sort expression>> to Vec<sort expression> #12195
Description
Consider AggregateFunction.order_by field -- it is Option<Vec< /*sort expr*/ >>
None means "no sorting" but this can be modeled as Some( vec![] ).
Empty collection perfectly describes lack of sorting, so no need to wrap if with optional value.
Remove Option and keep just Vec.
This can be applied to
AggregateFunction.order_byExprFuncBuilder.order_by- ...
based on #12178 (comment) cc @crepererum