[K/N] Fix ExtraObjectData not being collected ^KT-63423

kotlin-native/runtime/src/alloc/custom/cpp/AllocatorImpl.cpp

@@ -78,5 +78,13 @@ size_t alloc::allocatedBytes() noexcept {
 
 void alloc::destroyExtraObjectData(mm::ExtraObjectData& extraObject) noexcept {
     extraObject.ReleaseAssociatedObject();
-    extraObject.setFlag(mm::ExtraObjectData::FLAGS_FINALIZED);
+    if (extraObject.GetBaseObject()) {
+        // If there's an object attached to this extra object, the next
+        // GC sweep will have to resolve this cycle.
+        extraObject.setFlag(mm::ExtraObjectData::FLAGS_FINALIZED);
+    } else {
+        // If there's no object attached to this extra object, the next
+        // GC sweep will just collect this extra object.
+        extraObject.setFlag(mm::ExtraObjectData::FLAGS_SWEEPABLE);
+    }
 }

kotlin-native/runtime/src/alloc/custom/cpp/GCApi.cpp

@@ -78,9 +78,11 @@ bool SweepObject(uint8_t* object, FinalizerQueue& finalizerQueue, gc::GCHandle::
 
 bool SweepExtraObject(mm::ExtraObjectData* extraObject, gc::GCHandle::GCSweepExtraObjectsScope& gcHandle) noexcept {
     if (extraObject->getFlag(mm::ExtraObjectData::FLAGS_SWEEPABLE)) {
+        gcHandle.addSweptObject();
         CustomAllocDebug("SweepExtraObject(%p): can be reclaimed", extraObject);
         return false;
     }
+    gcHandle.addKeptObject(sizeof(mm::ExtraObjectData));
     CustomAllocDebug("SweepExtraObject(%p): is still needed", extraObject);
     return true;
 }