Added Navigation.constants() return type (#5292)

lib/src/Navigation.ts

 import { ComponentProvider } from 'react-native';
 import { SharedElement } from './adapters/SharedElement';
 import { CommandsObserver } from './events/CommandsObserver';
-import { Constants } from './adapters/Constants';
+import { Constants, NavigationConstants } from './adapters/Constants';
 import { ComponentEventsObserver } from './events/ComponentEventsObserver';
 import { TouchablePreview } from './adapters/TouchablePreview';
 import { LayoutRoot, Layout } from './interfaces/Layout';
   /**
    * Constants coming from native
    */
-  public async constants(): Promise<any> {
+  public async constants(): Promise<NavigationConstants> {
     return await Constants.get();
   }
 }