Rewrite imports in RNTester to use standard paths (#24317)

Summary:
See https://github.com/facebook/react-native/issues/24316 for the motivation. This commit rewrites the imports in the RNTester project.

[General] [Changed] - Replaced Haste-style imports with standard path-style imports for RNTester
Pull Request resolved: https://github.com/facebook/react-native/pull/24317

Differential Revision: D14870504

Pulled By: cpojer

fbshipit-source-id: b14f22e7ce559efc332ced032617ca581196d90f

RNTester/js/AlertExample.js

@@ -10,8 +10,13 @@
 'use strict';
 
 const React = require('react');
-const ReactNative = require('react-native');
-const {Alert, StyleSheet, Text, TouchableHighlight, View} = ReactNative;
+const {
+  Alert,
+  StyleSheet,
+  Text,
+  TouchableHighlight,
+  View,
+} = require('react-native');
 
 const RNTesterBlock = require('./RNTesterBlock');