Fix badgeColor for previous iOS 10 versions

Summary:
The actual badgeColor prop causes the following error when run on device with a version inferior to iOS 10 like iPad 2 and iPad mini 1.

`*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UITabBarItem setBadgeColor:]: unrecognized selector sent to instance 0x7968be80'`

This PR fixes it by checking at runtime if the selector is available for the current running version.

It also makes the color available at start by using the variable `self.barItem`. Currently, the color appears only after a reload.
Closes https://github.com/facebook/react-native/pull/12354

Differential Revision: D4598036

Pulled By: shergin

fbshipit-source-id: 9f104fc27db51213a54273e33c5a22f1b350c55e

React/Views/RCTTabBarItem.m

@@ -107,9 +107,10 @@ RCT_ENUM_CONVERTER(UITabBarSystemItem, (@{
 
 - (void)setBadgeColor:(UIColor *)badgeColor
 {
-#if !TARGET_OS_TV && defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_10_0
-  _barItem.badgeColor = badgeColor;
-#endif
+  // badgeColor available since iOS 10
+  if ([self.barItem respondsToSelector:@selector(badgeColor)]) {
+    self.barItem.badgeColor = badgeColor;
+  }
 }
 
 - (UIViewController *)reactViewController