Allow the app to control the Activity Indicator in Bridgeless mode

Summary:
Right now, the activity indicator is automatically hidden when the view is ready to be shown in bridgeless mode.
There is no way to prevent that the activity indicator is automatically removed.

In OSS, we have libraries (e.g.: `react-native-bootsplash`) that will allow the app to control when and how dismiss the splashscreen, but due to the current automatic behavior on Bridgeless, they stopped working.

***Note:** In the previous implementation, they were working because instead of using the `loadingView` property, they were adding the splashscreen view on top of the existing one. However, with the lazy behavior of the bridgeless mode, this is not working anymore because the RCTMountingManager [expect not to have any subview](https://www.internalfb.com/code/fbsource/[6962fa457dbc74ab3a760cf6090d9643c6748781]/xplat/js/react-native-github/packages/react-native/React/Fabric/Mounting/RCTMountingManager.mm?lines=176) when the first surface is mounted.*

## Changelog
[iOS][Added] - Allow the activityIndicator to be controlled from JS in bridgeless mode

Differential Revision: D54191856

packages/react-native/React/Base/Surface/SurfaceHostingView/RCTSurfaceHostingView.h

@@ -56,6 +56,12 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @property (nonatomic, copy, nullable) RCTSurfaceHostingViewActivityIndicatorViewFactory activityIndicatorViewFactory;
 
+/**
+ * When set to `YES`, the activity indicator is not automatically hidden when the Surface stage changes.
+ * In this scenario, users should invoke `hideActivityIndicator` to remove it.
+ * Defaults to `NO` for backward compatibility.
+ */
+@property (nonatomic, assign) BOOL preventActivityIndicatorAutoHide;
 @end
 
 NS_ASSUME_NONNULL_END

packages/react-native/React/Base/Surface/SurfaceHostingView/RCTSurfaceHostingView.mm

@@ -36,6 +36,7 @@ - (instancetype)initWithSurface:(id<RCTSurfaceProtocol>)surface
   if (self = [super initWithFrame:CGRectZero]) {
     _surface = surface;
     _sizeMeasureMode = sizeMeasureMode;
+    _preventActivityIndicatorAutoHide = NO;
 
     _surface.delegate = self;
     _stage = surface.stage;
@@ -142,7 +143,7 @@ - (void)setIsActivityIndicatorViewVisible:(BOOL)visible
       _activityIndicatorView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
       [self addSubview:_activityIndicatorView];
     }
-  } else {
+  } else if (!_preventActivityIndicatorAutoHide) {
     [_activityIndicatorView removeFromSuperview];
     _activityIndicatorView = nil;
   }
@@ -162,7 +163,16 @@ - (void)setIsSurfaceViewVisible:(BOOL)visible
     _surfaceView = _surface.view;
     _surfaceView.frame = self.bounds;
     _surfaceView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
-    [self addSubview:_surfaceView];
+    if (_activityIndicatorView && _preventActivityIndicatorAutoHide) {
+      // The activity indicator is still showing and the surface is set to
+      // prevent the auto hide. This means that the application will take care of
+      // hiding it when it's ready.
+      // Let's add the surfaceView below the activity indicator so it's ready once
+      // the activity indicator is hidden.
+      [self insertSubview:_surfaceView belowSubview:_activityIndicatorView];
+    } else {
+      [self addSubview:_surfaceView];
+    }
   } else {
     [_surfaceView removeFromSuperview];
     _surfaceView = nil;