Function add_sort_above 

pub fn add_sort_above<T: Clone + Default>(
    node: PlanContext<T>,
    sort_requirements: LexRequirement,
    fetch: Option<usize>,
) -> PlanContext<T>

This utility function adds a SortExec above an operator according to the given ordering requirements while preserving the original partitioning.

Note that this updates the plan in both the PlanContext.children and the PlanContext.plan’s children. Therefore its not required to sync the child plans with PlanContext::update_plan_from_children.