The library name is BCTextEngine and it includes a custom view named BBCodeView.
BBCodeView doesn't raise such an event.
You can take BBCodeView class from the b4xlib (it is a zip file), rename it to BBCodeView2 and add it to your project. This will allow you to modify it and add scrolling events.
Note that you will need to set BBCodeView2.TextEngine. It will not be set automatically.