How MvxTabbedPage gets the CurrentLy Presented Children content
## 💬 Questions and Help

MvxTabbedPage how to get the current display of Children content, I set TabIndex, SelectedItem at MvxTabbedPage, but both settings are invalid, toggling Content under Children will not trigger this change
![image](https://user-images.githubusercontent.com/9816794/163725257-09ce3b92-8664-40a8-a117-a0a45167e6a5.png)
![image](https://user-images.githubusercontent.com/9816794/163725282-cc687d83-58e4-449a-8735-71209f09cc76.png)

MvvmCross version:8.0.2
