fix: add missing collect_columns import in projection.rs

Author: yashrb24

datafusion/physical-plan/src/projection.rs

@@ -50,6 +50,7 @@ use datafusion_execution::TaskContext;
 use datafusion_expr::ExpressionPlacement;
 use datafusion_physical_expr::equivalence::ProjectionMapping;
 use datafusion_physical_expr::projection::Projector;
+use datafusion_physical_expr::utils::collect_columns;
 use datafusion_physical_expr_common::physical_expr::{PhysicalExprRef, fmt_sql};
 use datafusion_physical_expr_common::sort_expr::{
     LexOrdering, LexRequirement, PhysicalSortExpr,