Drain removable nodes on Reanimated commits

ReanimatedMountHook skipped handleNodeRemovals on Reanimated's own
commits. While CSS animations run, every mount carries the mount trait,
so the cleanup never ran for the duration of the animation. Tearing the
view tree down mid-animation then leaked the unmounted nodes (and their
still-scheduled CSS animations) in all update registries on Android.

Always run handleNodeRemovals; gate only the commit-unpause on React
commits.

Author: MatiPl01

packages/react-native-reanimated/Common/cpp/reanimated/Fabric/ReanimatedMountHook.cpp

@@ -26,24 +26,31 @@ void ReanimatedMountHook::shadowTreeDidMount(
   auto reaShadowNode = std::reinterpret_pointer_cast<ReanimatedCommitShadowNode>(
       std::const_pointer_cast<RootShadowNode>(rootShadowNode));
 
-  if (reaShadowNode->hasReanimatedMountTrait()) {
-    // We mark reanimated commits with ReanimatedMountTrait. We don't want other
-    // shadow nodes to use this trait, but since this rootShadowNode is Shared,
-    // we don't have that guarantee. That's why we also unset this trait in the
-    // commit hook. We remove it here mainly for the sake of cleanliness.
+  // We mark reanimated commits with ReanimatedMountTrait. We don't want other
+  // shadow nodes to use this trait, but since this rootShadowNode is Shared,
+  // we don't have that guarantee. That's why we also unset this trait in the
+  // commit hook. We remove it here mainly for the sake of cleanliness.
+  const bool isReanimatedMount = reaShadowNode->hasReanimatedMountTrait();
+  if (isReanimatedMount) {
     reaShadowNode->unsetReanimatedMountTrait();
-    return;
   }
 
   {
     auto lock = updatesRegistryManager_->lock();
+
+    // Always drain removable nodes, even on Reanimated's own commits. While CSS
+    // animations run every mount carries the mount trait, so returning early here
+    // would skip removals for the whole animation and leak unmounted nodes if the
+    // tree is torn down mid-animation.
     updatesRegistryManager_->handleNodeRemovals(*rootShadowNode);
 
-    // When commit from React Native has finished, we reset the skip commit flag
-    // in order to allow Reanimated to commit its tree
-    updatesRegistryManager_->unpauseReanimatedCommits();
-    if (updatesRegistryManager_->shouldCommitAfterPause()) {
-      requestFlush_();
+    if (!isReanimatedMount) {
+      // When a commit from React Native has finished, we reset the skip commit
+      // flag in order to allow Reanimated to commit its tree.
+      updatesRegistryManager_->unpauseReanimatedCommits();
+      if (updatesRegistryManager_->shouldCommitAfterPause()) {
+        requestFlush_();
+      }
     }
   }
 }