chore: use es6 import for SafeAreaView component (facebook#29143)

Summary:
This PR is to help proceed this discussion. react-native-community/discussions-and-proposals#201 (comment)

Converted `require` to `import` for SafeAreaView.

## Changelog

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[General] [Changed] - switched to es6 import for SafeAreaView
Pull Request resolved: facebook#29143

Test Plan: Tested that App runs on RNTester

Reviewed By: shergin

Differential Revision: D22109435

Pulled By: TheSavior

fbshipit-source-id: 57dc4ab88bf497b43422b20416afbe4c4a1e001d

Libraries/Components/SafeAreaView/SafeAreaView.js

@@ -8,9 +8,9 @@
  * @format
  */
 
-const Platform = require('../../Utilities/Platform');
-const React = require('react');
-const View = require('../View/View');
+import Platform from '../../Utilities/Platform';
+import * as React from 'react';
+import View from '../View/View';
 
 import type {HostComponent} from '../../Renderer/shims/ReactNativeTypes';
 import type {ViewProps} from '../View/ViewPropTypes';