Fix crash on HeadlessJsTaskService on old architecture (#48124)

Summary:
Pull Request resolved: #48124

Fixes #47592

The logic in HeadlessJsTaskService is broken. We should not check whether `getReactContext` is null or not.
Instead we should use the `enableBridgelessArchitecture` feature flag to understand if New Architecture was enabled or not.

The problem we were having is that `HeadlessJsTaskService` was attempting to load the New Architecture even if the user would have it turned off. The Service would then die attempting to load `libappmodules.so` which was correctly missing.

Changelog:
[Android] [Fixed] - Fix crash on HeadlessJsTaskService on old architecture

Reviewed By: javache

Differential Revision: D66826271

fbshipit-source-id: 2b8418e0b01b65014cdbfd0ec2f843420a15f9db

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/HeadlessJsTaskService.java

@@ -179,31 +179,30 @@ protected ReactContext getReactContext() {
   }
 
   private void createReactContextAndScheduleTask(final HeadlessJsTaskConfig taskConfig) {
-    final ReactHost reactHost = getReactHost();
-
-    if (reactHost == null) { // old arch
-      final ReactInstanceManager reactInstanceManager =
-          getReactNativeHost().getReactInstanceManager();
-
-      reactInstanceManager.addReactInstanceEventListener(
+    if (ReactNativeFeatureFlags.enableBridgelessArchitecture()) {
+      final ReactHost reactHost = getReactHost();
+      reactHost.addReactInstanceEventListener(
           new ReactInstanceEventListener() {
             @Override
             public void onReactContextInitialized(@NonNull ReactContext reactContext) {
               invokeStartTask(reactContext, taskConfig);
-              reactInstanceManager.removeReactInstanceEventListener(this);
+              reactHost.removeReactInstanceEventListener(this);
             }
           });
-      reactInstanceManager.createReactContextInBackground();
-    } else { // new arch
-      reactHost.addReactInstanceEventListener(
+      reactHost.start();
+    } else {
+      final ReactInstanceManager reactInstanceManager =
+          getReactNativeHost().getReactInstanceManager();
+
+      reactInstanceManager.addReactInstanceEventListener(
           new ReactInstanceEventListener() {
             @Override
             public void onReactContextInitialized(@NonNull ReactContext reactContext) {
               invokeStartTask(reactContext, taskConfig);
-              reactHost.removeReactInstanceEventListener(this);
+              reactInstanceManager.removeReactInstanceEventListener(this);
             }
           });
-      reactHost.start();
+      reactInstanceManager.createReactContextInBackground();
     }
   }
 }