Fix LayoutAnimation crash from mutation sort ordering (#56629)

Summary:
Pull Request resolved: #56629

`LayoutAnimationDriver::animationMutationsForFrame` was sorting animation-frame Update mutations together with structural mutations (Remove/Insert/Delete) from completed animations. Animation-frame Updates reference views by their pre-structural-change parentTag. When `std::stable_sort` reordered these Updates after Remove/Insert pairs that reparented a view, `StubViewTree::mutate` hit a parentTag mismatch assertion (`react_native_assert(oldStubView->parentTag == mutation.parentTag)`) and crashed with SIGABRT.

The fix records the boundary between animation-frame Updates and final structural mutations, then only sorts the structural portion. This preserves the invariant that animation-frame Updates execute before any structural changes.

Per zeyap's review: simplified to just the LayoutAnimationDriver.cpp change. The earlier MutationComparator (`Update < Insert`) tweak and the `TEST_F` + feature-flag test refactor were dropped — the driver-side fix alone unbreaks the failing test.

Changelog: [Internal]

Reviewed By: zeyap

Differential Revision: D102696875

fbshipit-source-id: abaac2ae6dae44f7df1f4088bb8ec19b055c2b1a

Author: fkgozali

packages/react-native/ReactCommon/react/renderer/animations/LayoutAnimationDriver.cpp

@@ -74,6 +74,10 @@ void LayoutAnimationDriver::animationMutationsForFrame(
     }
   }
 
+  // Record boundary: animation-frame Updates above this point carry
+  // parentTag from before any structural changes and must execute first.
+  auto animationUpdatesEnd = mutationsList.size();
+
   // Clear out finished animations
   for (auto it = inflightAnimations_.begin();
        it != inflightAnimations_.end();) {
@@ -99,10 +103,11 @@ void LayoutAnimationDriver::animationMutationsForFrame(
     }
   }
 
-  // Final step: make sure that all operations execute in the proper order.
-  // REMOVE operations with highest indices must operate first.
+  // Sort only the final mutations from completed animations.
+  // Animation-frame Updates must stay before structural mutations because
+  // they reference views by their pre-structural-change parentTag.
   std::stable_sort(
-      mutationsList.begin(),
+      mutationsList.begin() + static_cast<ptrdiff_t>(animationUpdatesEnd),
       mutationsList.end(),
       &shouldFirstComeBeforeSecondMutation);
 }