rn: adapt to API changes in google signin

react/features/google-api/googleApi.native.js

@@ -35,6 +35,15 @@ class GoogleApi {
         }
     }
 
+    /**
+     * Retrieves the current tokens.
+     *
+     * @returns {Promise}
+     */
+    getTokens(): Promise<*> {
+        return GoogleSignin.getTokens();
+    }
+
     /**
      * Retrieves the available YouTube streams the user can use for live
      * streaming.