Cocos-2dx疑难集锦

让DrawNode支持Opacity

• Issue
  https://github.com/cocos2d/cocos2d-x/pull/17248

• 代码详情
  https://github.com/cocos2d/cocos2d-x/pull/17248/commits/b425bd7e470fefa497e96b9dbec7db778880e5cb
  https://github.com/cocos2d/cocos2d-x/pull/17324/commits/f29d51f2c36001f69843e38e7c87a0ba323fa812

让RichText支持获取所有文字

• 详见教程RichText仿Label::getLetter()获取所有文字