Fixed HashSet compaction count after mid-compact growth

Ensure HashSetBase::Compact() preserves _elementsCount even when EnsureCapacity() triggers during compaction. The growth path resets the counter; we now cache the original count and restore it after moving all buckets so Count() stays correct in heavy-collision scenarios.

Source/Engine/Core/Collections/HashSetBase.h

@@ -408,6 +408,7 @@ protected:
         }
         else
         {
+            const int32 elementsCount = _elementsCount;
             // Rebuild entire table completely
             const int32 oldSize = _size;
             AllocationData oldAllocation;
@@ -437,6 +438,7 @@ protected:
             }
             for (int32 i = 0; i < oldSize; ++i)
                 oldData[i].Free();
+            _elementsCount = elementsCount;
         }
         _deletedCount = 0;
     }