Fix crash in fixMountingCoordinatorReportedPendingTransactionsOnAndroid feature flag (facebook#50088)

Summary:
Pull Request resolved: facebook#50088

Changelog: [internal]

This fixes a crash when using the `fixMountingCoordinatorReportedPendingTransactionsOnAndroid` feature flag. The problem was that we were accessing the surface handler registry safely, but there were cases where invalid surface handler references were being kept in the registry.

Reviewed By: javache

Differential Revision: D71387111

fbshipit-source-id: 643fcdf10c4c5751d77e276efb37795b7af726bb

Author: rubennorte

packages/react-native/ReactAndroid/src/main/jni/react/fabric/FabricUIManagerBinding.cpp

@@ -318,6 +318,15 @@ void FabricUIManagerBinding::stopSurfaceWithSurfaceHandler(
         << this << ", surfaceId: " << surfaceHandler.getSurfaceId() << ").";
   }
 
+  // This is necessary to make sure we remove the surface handler from the
+  // registry before invalidating it. Otherwise, we can access an invalid
+  // reference in `reportMount`.
+  if (ReactNativeFeatureFlags::
+          fixMountingCoordinatorReportedPendingTransactionsOnAndroid()) {
+    std::unique_lock lock(surfaceHandlerRegistryMutex_);
+    surfaceHandlerRegistry_.erase(surfaceHandler.getSurfaceId());
+  }
+
   surfaceHandler.stop();
 
   auto scheduler = getScheduler();
@@ -328,7 +337,8 @@ void FabricUIManagerBinding::stopSurfaceWithSurfaceHandler(
   }
   scheduler->unregisterSurface(surfaceHandler);
 
-  {
+  if (!ReactNativeFeatureFlags::
+          fixMountingCoordinatorReportedPendingTransactionsOnAndroid()) {
     std::unique_lock lock(surfaceHandlerRegistryMutex_);
     surfaceHandlerRegistry_.erase(surfaceHandler.getSurfaceId());
   }