ConcurrentModificationException while working with composition items.…

… Code refactoring jmix-framework#1350

It will also fix original problem but other problems will eventually occur for custom equals and hashCode implementations

jmix-data/eclipselink/src/main/java/io/jmix/eclipselink/impl/EclipselinkPersistenceSupport.java

@@ -422,7 +422,7 @@ protected void unregisterInstance(Object instance, UnitOfWork unitOfWork, String
         }
 
         protected Collection<Object> getInstances(UnitOfWork unitOfWork, String store) {
-            Set<Object> set = new HashSet<>();
+            Set<Object> set = createEntitySet();
             Map<UnitOfWork, Set<Object>> unitOfWorkMap = unitsOfWorkToStores.get(store);
             if (unitOfWorkMap != null) {
                 Set<Object> entities = unitOfWorkMap.get(unitOfWork);