Function find_base_plan

pub fn find_base_plan(input: &LogicalPlan) -> &LogicalPlan

Find the suitable base plan to expand the wildcard expression recursively. When planning LogicalPlan::Window and LogicalPlan::Aggregate, we will generate an intermediate plan based on the relation plan (e.g. LogicalPlan::TableScan, LogicalPlan::Subquery, …). If we expand a wildcard expression basing the intermediate plan, we could get some duplicate fields.