[FEAT MERGE] DAS iterator refactor and keep order optimization

Co-authored-by: saltonz <saltonzh@gmail.com>
Co-authored-by: zhenhan.gong@gmail.com <zhenhan.gong@gmail.com>
Co-authored-by: Tyshawn <tuyunshan@gmail.com>

src/sql/ob_optimizer_trace_impl.cpp

@@ -937,6 +937,7 @@ int ObOptimizerTraceImpl::trace_parameters()
     TRACE_PARAMETER(_optimizer_sortmerge_join_enabled, bool);
     TRACE_PARAMETER(_nested_loop_join_enabled, bool);
     TRACE_PARAMETER(_enable_var_assign_use_das, bool);
+    TRACE_PARAMETER(_enable_das_keep_order, bool);
     //for system variables
     TRACE_SYS_VAR(_PX_SHARED_HASH_JOIN, int64_t);
     TRACE_SYS_VAR(_ENABLE_PARALLEL_DML, int64_t);