[fix] convert VirtualizedList vendor code to ES modules

Webpack has trouble bundling a mix of CommonJS and ES modules in the
same package.

Fix #957

packages/react-native-web/src/vendor/Batchinator/index.js

@@ -70,4 +70,4 @@ class Batchinator {
   }
 }
 
-module.exports = Batchinator;
+export default Batchinator;

packages/react-native-web/src/vendor/FillRateHelper/index.js

@@ -8,16 +8,8 @@
  * @format
  */
 
-'use strict';
-
-/* $FlowFixMe(>=0.54.0 site=react_native_oss) This comment suppresses an error
- * found when Flow v0.54 was deployed. To see the error delete this comment and
- * run Flow. */
-const performanceNow = require('fbjs/lib/performanceNow');
-/* $FlowFixMe(>=0.54.0 site=react_native_oss) This comment suppresses an error
- * found when Flow v0.54 was deployed. To see the error delete this comment and
- * run Flow. */
-const warning = require('fbjs/lib/warning');
+import performanceNow from 'fbjs/lib/performanceNow';
+import warning from 'fbjs/lib/warning';
 
 export type FillRateInfo = Info;
 
@@ -221,4 +213,4 @@ class FillRateHelper {
   }
 }
 
-module.exports = FillRateHelper;
+export default FillRateHelper;

packages/react-native-web/src/vendor/ViewabilityHelper/index.js

@@ -7,9 +7,8 @@
  * @noflow
  * @format
  */
-'use strict';
 
-const invariant = require('fbjs/lib/invariant');
+import invariant from 'fbjs/lib/invariant';
 
 export type ViewToken = {
   item: any,
@@ -275,4 +274,4 @@ function _isEntirelyVisible(top: number, bottom: number, viewportHeight: number)
   return top >= 0 && bottom <= viewportHeight && bottom > top;
 }
 
-module.exports = ViewabilityHelper;
+export default ViewabilityHelper;

packages/react-native-web/src/vendor/VirtualizeUtils/index.js

@@ -7,16 +7,15 @@
  * @flow
  * @format
  */
-'use strict';
 
-const invariant = require('fbjs/lib/invariant');
+import invariant from 'fbjs/lib/invariant';
 
 /**
  * Used to find the indices of the frames that overlap the given offsets. Useful for finding the
  * items that bound different windows of content, such as the visible area or the buffered overscan
  * area.
  */
-function elementsThatOverlapOffsets(
+export function elementsThatOverlapOffsets(
   offsets: Array<number>,
   itemCount: number,
   getFrameMetrics: (index: number) => { length: number, offset: number }
@@ -50,7 +49,7 @@ function elementsThatOverlapOffsets(
  * can restrict the number of new items render at once so that content can appear on the screen
  * faster.
  */
-function newRangeCount(
+export function newRangeCount(
   prev: { first: number, last: number },
   next: { first: number, last: number }
 ): number {
@@ -68,7 +67,7 @@ function newRangeCount(
  * prioritizes the visible area first, then expands that with overscan regions ahead and behind,
  * biased in the direction of scroll.
  */
-function computeWindowedRenderLimits(
+export function computeWindowedRenderLimits(
   props: {
     data: any,
     getItemCount: (data: any) => number,
@@ -201,4 +200,4 @@ const VirtualizeUtils = {
   newRangeCount
 };
 
-module.exports = VirtualizeUtils;
+export default VirtualizeUtils;

packages/react-native-web/src/vendor/VirtualizedList/index.js

@@ -1593,4 +1593,4 @@ const styles = StyleSheet.create({
   }
 });
 
-module.exports = VirtualizedList;
+export default VirtualizedList;