docs(analytics): update screen tracking example (#5564)

* Updating screen tracking example

Updating screen tracking example documentation to include full example. Also removed ``state`` and ``getActiveRouteName`` as you need to create that function to extract active route name from the state. The idea is for someone to quickly use the example without trying to figure out what does ``getActiveRouteName`` and where is it defined.

Co-authored-by: Mike Hardy <[email protected]>

Author: Thagana

docs/analytics/screen-tracking.md

@@ -20,18 +20,34 @@ method the Analytics library provides:
 import analytics from '@react-native-firebase/analytics';
 import { NavigationContainer } from '@react-navigation/native';
 
-<NavigationContainer
-  ref={navigationRef}
-  onStateChange={async (state) => {
-    const previousRouteName = routeNameRef.current;
-    const currentRouteName = getActiveRouteName(state);
-
-    if (previousRouteName !== currentRouteName) {
-      await analytics().logScreenView({
-        screen_name: currentRouteName,
-        screen_class: currentRouteName,
-      });
-    }
+const App = () => {
+  const routeNameRef = React.useRef();
+  const navigationRef = React.useRef();
+  return (
+    <NavigationContainer
+      ref={navigationRef}
+      onReady={() => {
+        routeNameRef.current = navigationRef.current.getCurrentRoute().name;
+      }}
+      onStateChange={async () => {
+        const previousRouteName = routeNameRef.current;
+        const currentRouteName = navigationRef.current.getCurrentRoute().name;
+
+        if (previousRouteName !== currentRouteName) {
+          await analytics().logScreenView({
+            screen_name: currentRouteName,
+            screen_class: currentRouteName,
+          });
+        }
+        routeNameRef.current = currentRouteName;
+      }}
+    >
+      ...
+    </NavigationContainer>
+  );
+};
+
+export default App;
 ```
 
 For a full working example, view the [Screen tracking for analytics](https://reactnavigation.org/docs/screen-tracking/)