ReactFragment should properly instantiate ReactDelegate on Bridgeless (#46623)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/46623

I've just noticed that ReactFragment is not properly instantiating the `ReactDelegate` with a ReactHost
when on Bridgeless. This causes Fragments to crash when the app is on bridgeless mode.

Fixes https://github.com/facebook/react-native/issues/46566

Changelog:
[Android] [Fixed] - ReactFragment should properly instantiate ReactDelegate on Bridgeless

Reviewed By: mdvacca

Differential Revision: D63319977

fbshipit-source-id: 08256e35b2769e18df2d24f870ec5d98e5574f85

packages/react-native/ReactAndroid/api/ReactAndroid.api

@@ -192,6 +192,7 @@ public class com/facebook/react/ReactFragment : androidx/fragment/app/Fragment,
 	public fun checkPermission (Ljava/lang/String;II)I
 	public fun checkSelfPermission (Ljava/lang/String;)I
 	protected fun getReactDelegate ()Lcom/facebook/react/ReactDelegate;
+	protected fun getReactHost ()Lcom/facebook/react/ReactHost;
 	protected fun getReactNativeHost ()Lcom/facebook/react/ReactNativeHost;
 	public fun onActivityResult (IILandroid/content/Intent;)V
 	public fun onBackPressed ()Z

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

@@ -17,6 +17,7 @@ import android.view.ViewGroup;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.fragment.app.Fragment;
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlags;
 import com.facebook.react.modules.core.PermissionAwareActivity;
 import com.facebook.react.modules.core.PermissionListener;
 
@@ -80,9 +81,14 @@ public class ReactFragment extends Fragment implements PermissionAwareActivity {
     if (mainComponentName == null) {
       throw new IllegalStateException("Cannot loadApp if component name is null");
     }
-    mReactDelegate =
-        new ReactDelegate(
-            getActivity(), getReactNativeHost(), mainComponentName, launchOptions, fabricEnabled);
+    if (ReactNativeFeatureFlags.enableBridgelessArchitecture()) {
+      mReactDelegate =
+          new ReactDelegate(getActivity(), getReactHost(), mainComponentName, launchOptions);
+    } else {
+      mReactDelegate =
+          new ReactDelegate(
+              getActivity(), getReactNativeHost(), mainComponentName, launchOptions, fabricEnabled);
+    }
   }
 
   /**
@@ -92,8 +98,34 @@ public class ReactFragment extends Fragment implements PermissionAwareActivity {
    * implement {@code ReactApplication} or you simply have a different mechanism for storing a
    * {@code ReactNativeHost}, e.g. as a static field somewhere.
    */
+  @Nullable
   protected ReactNativeHost getReactNativeHost() {
-    return ((ReactApplication) getActivity().getApplication()).getReactNativeHost();
+    ReactApplication application = ((ReactApplication) getActivity().getApplication());
+    if (application != null) {
+      return application.getReactNativeHost();
+    } else {
+      return null;
+    }
+  }
+
+  /**
+   * Get the {@link ReactHost} used by this app. By default, assumes {@link
+   * Activity#getApplication()} is an instance of {@link ReactApplication} and calls {@link
+   * ReactApplication#getReactHost()}. Override this method if your application class does not
+   * implement {@code ReactApplication} or you simply have a different mechanism for storing a
+   * {@code ReactHost}, e.g. as a static field somewhere.
+   *
+   * <p>If you're using Old Architecture/Bridge Mode, this method should return null as {@link
+   * ReactHost} is a Bridgeless-only concept.
+   */
+  @Nullable
+  protected ReactHost getReactHost() {
+    ReactApplication application = ((ReactApplication) getActivity().getApplication());
+    if (application != null) {
+      return application.getReactHost();
+    } else {
+      return null;
+    }
   }
 
   protected ReactDelegate getReactDelegate() {