It is possible to add a Visual Editor to a plugin to use, but that is done at the coding level (so the plugin needs to be altered). I recently did it with 2 of my plugins. The only way to do code is to switch from the Visual Editor to the code editor. While you won't see the code in the Visual Editor, it's still there if you added it in the code editor. There isn't a Visual/Code editor out there that I know of that gracefully accepts code and can simply visually add things to your post--I suspect they would battle each other and not work very well.