Merge pull request #21615 from No-Plane-Cannot-Be-Detected:5.x-ptcloud_comments

Added 3D point cloud code comments and copyright

1. update the code comments.
2. add author information.

modules/3d/test/test_sampling.cpp

@@ -1,6 +1,8 @@
 // This file is part of OpenCV project.
 // It is subject to the license terms in the LICENSE file found in the top-level directory
 // of this distribution and at http://opencv.org/license.html.
+//
+// Copyright (C) 2021, Wanli Zhong <zhongwl2018@mail.sustech.edu.cn>
 
 #include "test_precomp.hpp"