Expose statusBarHeight in Navigation.constants

lib/android/app/src/main/java/com/reactnativenavigation/react/Constants.java

 public class Constants {
     public static final String BACK_BUTTON_JS_KEY = "backButton";
     public static final String BACK_BUTTON_ID = "RNN.back";
+    public static final String STATUS_BAR_HEIGHT_KEY = "statusBarHeight";
 }

lib/android/app/src/main/java/com/reactnativenavigation/react/NavigationModule.java

 import com.reactnativenavigation.utils.Now;
 import com.reactnativenavigation.utils.TypefaceLoader;
 import com.reactnativenavigation.utils.UiThread;
+import com.reactnativenavigation.utils.UiUtils;
 import com.reactnativenavigation.viewcontrollers.Navigator;
 import com.reactnativenavigation.viewcontrollers.ViewController;
 import com.reactnativenavigation.viewcontrollers.externalcomponent.ExternalComponentCreator;
     public Map<String, Object> getConstants() {
         final Map<String, Object> constants = new HashMap<>();
         constants.put(Constants.BACK_BUTTON_JS_KEY, Constants.BACK_BUTTON_ID);
+        constants.put(Constants.STATUS_BAR_HEIGHT_KEY, UiUtils.getStatusBarHeight(getReactApplicationContext()));
         return constants;
     }
 

lib/src/constants/Constants.test.ts

 import { Constants } from './Constants';
 
 const NavigationModule = {
-  backButton: 'backButton'
+  backButton: 'RNN.back',
+  statusBarHeight: 63
 };
 
 describe('Constants', () => {
   it('backButton', () => {
     expect(uut.backButton).toEqual(NavigationModule.backButton);
   });
+
+  it('statusBarHeight', () => {
+    expect(uut.statusBarHeight).toEqual(NavigationModule.statusBarHeight);
+  });
 });

lib/src/constants/Constants.ts

 export class Constants {
   public readonly backButton;
+  public readonly statusBarHeight;
 
   constructor(navigationModule) {
     this.backButton = navigationModule.backButton;
+    this.statusBarHeight = navigationModule.statusBarHeight;
   }
 }