Add bluring inputs on disactivating screen

[osdnk]

Motivation

This a solution for https://github.com/kmagiera/react-native-screens/issues/67

Keyboard doesn't dismiss after navigating to another screen and back. Even on Keyboard.dismiss() call. It seems like without Screens keyboard is dismissed on every navigation.

Repo: snack.expo.io/@andrey/keyboard-bug Focus TextInput -> Next Screen -> Back -> Keyboard is not dismissing

Changes

Before setting screen to inactive, I added walking through all subviews and checking whether it's TextInput. If yes, it's being blurred then.

[buoyad]

I can confirm this fixes the problem in iOS for us. ping @kmagiera do you think this can be merged?

[hirbod]

@WoLewicki can this maybe land into master?

[WoLewicki]

cc @osdnk