Merge 10.3 into 10.4

We will expose some more std::atomic internals in Atomic_counter,
so that dict_index_t::lock will support the default assignment operator.

sql/sql_statistics.cc

@@ -1671,6 +1671,7 @@ public:
   */
   virtual bool add()
   {
+    table_field->mark_unused_memory_as_defined();
     return tree->unique_add(table_field->ptr);
   }