Fix the memory bloat issue with the sort operator in the rescan scenario.

src/sql/engine/sort/ob_prefix_sort_vec_op_impl.h

@@ -36,7 +36,7 @@ public:
     selector_(nullptr), selector_size_(0), sort_prefix_rows_(0), prefix_pos_(0),
     im_sk_store_(&allocator_), im_addon_store_(&allocator_),
     im_sk_rows_(nullptr), im_addon_rows_(nullptr), immediate_pos_(0),
-    brs_(nullptr)
+    brs_(nullptr), brs_holder_(&allocator_)
   {}
   virtual ~ObPrefixSortVecImpl()
   {

src/sql/engine/sort/ob_prefix_sort_vec_op_impl.ipp

@@ -21,6 +21,7 @@ void ObPrefixSortVecImpl<Compare, Store_Row, has_addon>::reset()
   full_sk_collations_ = nullptr;
   base_sk_collations_.reset();
   brs_holder_.reset();
+  brs_holder_.destroy();
   next_prefix_row_ = nullptr;
   prev_row_ = nullptr;
   child_ = nullptr;