Fabric: More asserts in RCTMountingTransactionObserverCoordinator

Summary:
Just asserts to be sure that we don't over-insert or over-erase to/from the collection.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D18567732

fbshipit-source-id: 569dbce6e62380ae3a0716448ad10bf418aa4f9c

React/Fabric/Mounting/RCTMountingTransactionObserverCoordinator.mm

@@ -21,6 +21,7 @@ void RCTMountingTransactionObserverCoordinator::registerViewComponentDescriptor(
   }
 
   auto &surfaceRegistry = registry_[surfaceId];
+  assert(surfaceRegistry.count(componentViewDescriptor) == 0);
   surfaceRegistry.insert(componentViewDescriptor);
 }
 
@@ -34,6 +35,7 @@ void RCTMountingTransactionObserverCoordinator::unregisterViewComponentDescripto
   }
 
   auto &surfaceRegistry = registry_[surfaceId];
+  assert(surfaceRegistry.count(componentViewDescriptor) == 1);
   surfaceRegistry.erase(componentViewDescriptor);
 }