MDEV-32583 UUID() should be treated as stochastic for the purposes of forcing query materialization

Port 9e800eda changing lex->safe_to_cache_query
to lex->uncacheable(UNCACHEABLE_RAND).

plugin/type_uuid/plugin.cc

@@ -150,7 +150,7 @@ class Create_func_uuid_v4 : public Create_func_arg0
   {
     DBUG_ENTER("Create_func_uuid_v4::create");
     thd->lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_SYSTEM_FUNCTION);
-    thd->lex->safe_to_cache_query= 0;
+    thd->lex->uncacheable(UNCACHEABLE_RAND);
     DBUG_RETURN(new (thd->mem_root) Item_func_uuid_v4(thd));
   }
   static Create_func_uuid_v4 s_singleton;