Use stable_sort in lod_rank_table (#5378)

It is easy to debug and test when use `stable_sort`and the time
complexity is not changed.

paddle/framework/lod_rank_table.cc

@@ -33,7 +33,12 @@ void LoDRankTable::Reset(const LoD& lod, size_t level) {
     item.length = vec[i + 1] - vec[i];
     items_.emplace_back(item);
   }
-  std::sort(items_.begin(), items_.end(),
+  // NOTE(yuyang18):
+  //
+  // The time complexity of stable_sort is O(N*log(N)) if additional memory is
+  // available. It is easy to debug and unit test when using `stable_sort`
+  // instead of `sort`. Also, the items of a rank table will not be too large.
+  std::stable_sort(items_.begin(), items_.end(),
                    [](const TableItem& a, const TableItem& b) {
                      return a.length > b.length;
                    });