Resolve react flow definitions

Summary:Currently, we're not taking advantage of Flow's built-in type definitions for the React library in all cases because Flow's definition uses `declare module react` and this file uses `import('React')`, which Flow thinks is a different library. After this change, the following starts working which didn't before:

```js
import { Component } from 'react-native';

class MyText extends Component<void, {text: string}, void> {
  render() { return <Text>{this.props.text}</Text> }
}

// Correctly throws a Flow error for the missing "text" prop
const renderedText = <MyText />;
```
Closes https://github.com/facebook/react-native/pull/5489

Differential Revision: D2856176

fb-gh-sync-id: 473ca188ad7d990c3e765526c4b33caf49ad9ffd
shipit-source-id: 473ca188ad7d990c3e765526c4b33caf49ad9ffd

Examples/UIExplorer/NavigationExperimental/NavigationTicTacToeExample.js

@@ -98,6 +98,7 @@ function isGameOver(gameString: string): boolean {
 }
 
 class Cell extends React.Component {
+  props: any;
   cellStyle() {
     switch (this.props.player) {
       case 'X':
@@ -207,6 +208,9 @@ function GameReducer(lastGame: ?string, action: Object): string {
 }
 
 class NavigationTicTacToeExample extends React.Component {
+  static GameView = TicTacToeGame;
+  static GameReducer = GameReducer;
+  static GameActions = GameActions;
   render() {
     return (
       <NavigationRootContainer
@@ -222,9 +226,6 @@ class NavigationTicTacToeExample extends React.Component {
     );
   }
 }
-NavigationTicTacToeExample.GameView = TicTacToeGame;
-NavigationTicTacToeExample.GameReducer = GameReducer;
-NavigationTicTacToeExample.GameActions = GameActions;
 
 const styles = StyleSheet.create({
   closeButton: {