StatusBar: barStyle support for Android (API 23+)

Summary:
Android (starting from API 23) supports "light status bar", thus it is possible to extend StatusBar and make `barStyle` property work not only for iOS, but also for Android.

This PR introduces one more `barStyle` option `dark-content` in addition to two existing ones (`default` and `light-content`).
Why there are 3 options instead of 2?

Two simple reasons:
1) to make all existing applications fully compatible with these changes;
2) the default status bar on Android is dark with white text and icons, while on iOS it is light with black text and icons on it. Thus the `default` option means something like "I don't really care, just apply the default color for this platform", while two other options (`light-content` and `dark-content`) allow to accurately specify the required result.
Closes https://github.com/facebook/react-native/pull/10185

Differential Revision: D3952346

fbshipit-source-id: 999a67614abff52321fbeb06298ebf1946c3f1d1

ReactAndroid/src/main/java/com/facebook/react/modules/statusbar/StatusBarModule.java

@@ -170,4 +170,28 @@ public class StatusBarModule extends ReactContextBaseJavaModule {
         }
       });
   }
+
+  @ReactMethod
+  public void setStyle(final String style, final Promise res) {
+    final Activity activity = getCurrentActivity();
+    if (activity == null) {
+      res.reject(ERROR_NO_ACTIVITY, ERROR_NO_ACTIVITY_MESSAGE);
+      return;
+    }
+
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+      UiThreadUtil.runOnUiThread(
+        new Runnable() {
+          @TargetApi(Build.VERSION_CODES.M)
+          @Override
+          public void run() {
+            View decorView = activity.getWindow().getDecorView();
+            decorView.setSystemUiVisibility(
+              style.equals("dark-content") ? View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR : 0);
+            res.resolve(null);
+          }
+        }
+      );
+    }
+  }
 }