Provide iOS-compatible implementation for direction property #4668
Description
While investigating #4499 I started playing around with the direction property and found it doesn't work correctly.
To see this in action, see:
https://snack.expo.io/JV!BvpeCj
If you run this on iOS, the buttons and the Picker will flow RTL
If you run this on react-native-windows, the buttons will flow LTR, but the Picker will flow RTL
The basic problem is in RNW's code that handles the direction property. We let yoga do the layout in RTL, but then we set the FlowDirection property on the backing XAML element. This flips the RN children back to LTR. But a native component like Picker will still pick up the XAML RightToLeft. So you end up with a weird mix of LTR and RTL.
This bug is tracking fixing this by providing a "correct" implementation for direction. iOS does it correctly. We should too.