Fix native postMessage test

The current way we're testing if postMessage has been changed is no
longer valid. Lodash has already changed the way they test agianst this,
as it no longer works in blink (thow continiues to work in webkit)

In chrome browser (Version 65.0.3325.181 (Official Build) (64-bit)) console type:

```js
String(window.postMessage) === String(Object.hasOwnProperty).replace('hasOwnProperty', 'postMessage')
```

It still works in safari (Version 11.0.3 (13604.5.6))

A simplified version of how lodash are testing aginst it
https://github.com/lodash/lodash/blob/4.0.1-npm-packages/lodash.isnative/index.js

With a simpler description about this method can be found here:
https://davidwalsh.name/detect-native-function

Running:

```js
RegExp('^' +
  String(Object.prototype.toString)
  .replace(/[.*+?^${}()|[\]\/\\]/g, '\\$&')
  .replace(/toString|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$'
).test(String(window.postMessage))
```

Works correctly in both chrome and safari.

Affected issues:

facebook#10865 - some hacks were
seggested here to sidestep this issue. This PR should fix it outright

React/Views/RCTWebView.m

@@ -299,7 +299,7 @@ - (void)webViewDidFinishLoad:(UIWebView *)webView
   if (_messagingEnabled) {
     #if RCT_DEV
     // See isNative in lodash
-    NSString *testPostMessageNative = @"String(window.postMessage) === String(Object.hasOwnProperty).replace('hasOwnProperty', 'postMessage')";
+    NSString *testPostMessageNative = @"RegExp('^'+String(Object.prototype.toString).replace(/[.*+?^${}()|[\]\/\\]/g, '\\$&').replace(/toString|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$').test(String(window.postMessage))";
     BOOL postMessageIsNative = [
       [webView stringByEvaluatingJavaScriptFromString:testPostMessageNative]
       isEqualToString:@"true"

ReactAndroid/src/main/java/com/facebook/react/views/webview/ReactWebViewManager.java

@@ -305,7 +305,7 @@ public void linkBridge() {
       if (messagingEnabled) {
         if (ReactBuildConfig.DEBUG && Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
           // See isNative in lodash
-          String testPostMessageNative = "String(window.postMessage) === String(Object.hasOwnProperty).replace('hasOwnProperty', 'postMessage')";
+          String testPostMessageNative = "RegExp('^'+String(Object.prototype.toString).replace(/[.*+?^${}()|[\]\/\\]/g, '\\$&').replace(/toString|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$').test(String(window.postMessage))";
           evaluateJavascript(testPostMessageNative, new ValueCallback<String>() {
             @Override
             public void onReceiveValue(String value) {