[RFC][Rendering] Add shouldRasterizeIOS to View components

Summary:
Exposes the `shouldRasterize` property. Fixes #1986.
Closes https://github.com/facebook/react-native/pull/2226
Github Author: James Ide <ide@jameside.com>

Libraries/ReactNative/ReactNativeViewAttributes.js

@@ -23,6 +23,7 @@ ReactNativeViewAttributes.UIView = {
   accessibilityLiveRegion: true,
   accessibilityTraits: true,
   testID: true,
+  shouldRasterizeIOS: true,
   onLayout: true,
   onAccessibilityTap: true,
   onMagicTap: true,