add warning for StatusBarIOS (#25350)

Summary:
`StatusBarIOS` has been merged with `StatusBar`. See [Implement a StatusBar frame API](https://github.com/facebook/react-native/pull/16478)

## Changelog

[General] [Deprecate] -  Warning for `StatusBarIOS`
Pull Request resolved: https://github.com/facebook/react-native/pull/25350

Test Plan: Warning prints when user imports `StatusBarIOS`

Differential Revision: D15963347

Pulled By: cpojer

fbshipit-source-id: 456a7f3ccb245bd89ad322d5a2649e3bf844ba24

Libraries/react-native/react-native-implementation.js

@@ -251,6 +251,10 @@ module.exports = {
     return require('../Share/Share');
   },
   get StatusBarIOS() {
+    warnOnce(
+      'StatusBarIOS-merged',
+      'StatusBarIOS has been merged with StatusBar and will be removed in a future release. Use StatusBar for mutating the status bar',
+    );
     return require('../Components/StatusBar/StatusBarIOS');
   },
   get StyleSheet() {