Implement ChoicesBindingNameProperty

## 🚀 Feature Requests

ChoicesBindingNameProperty is currently commented out in the code. You cannot set it but there already is an implementation for it.

### Contextualize the feature
You can set any object as Choices but currently there is no option to specify which property of the object should be shown in the picker dialog.

### Describe the feature
There should be an option to specify a converter which receives the object from the list and returns a string for the dialog. For this the type of ChoicesBindingName needs to be changed to BindingBase.

Usage would be something like this:
```

```

### Platforms affected (mark all that apply)
- [x] :iphone: iOS
- [x] :robot: Android
- [x] :checkered_flag: WPF
- [x] :earth_americas: UWP
- [x] :apple: MacOS
- [x] :tv: tvOS
- [x] :monkey: Xamarin.Forms