Summary:
This PR adds e2e tests for the Picker and DatePicker components.
While writing these tests, I also found and fixed two bugs where we wern't passing the `testID` down to the native components, so detox couldn't look them up. This confirms what was mentioned by rotemmiz [here](https://github.com/wix/Detox/issues/798#issuecomment-401412276)
Pull Request resolved: https://github.com/facebook/react-native/pull/22537
Reviewed By: cpojer
Differential Revision: D13371307
Pulled By: rickhanlonii
fbshipit-source-id: a4dfcdb5913645bceca0c7353328eeb9ad0f6558