Dismiss the Keyboard when changing the page natively (Android)

[ferrannp]

This is already done in JS https://github.com/react-native-community/react-native-viewpager/blob/9a7b1a0a0528786832bd203e96e1826d2849b8fb/js/ViewPager.js#L106-L110

But we did it natively on iOS. Should be also easy to do it natively on Android: https://stackoverflow.com/a/11818992/2277631

[Relax594]

any ETA on this one?