Fix EntitySet enumerator behavior change caused by the Dictionary enumerator behavior change (See dotnet/runtime#26314)

Author: AlexUstinov

Orm/Xtensive.Orm.Tests/Issues/IssueJira0718_EntitySetEnumerationBug.cs

@@ -1024,7 +1024,7 @@ public void ClientProfileTest19()
         Assert.Throws<InvalidOperationException>(
           () => {
             foreach (var orderItem in customerOrder.Items)
-              customerOrder.Remove();
+              customerOrderItem.Remove();
           });
         transaction.Complete();
       }

Orm/Xtensive.Orm/Orm/Internals/EntitySetState.cs

@@ -298,21 +298,37 @@ protected override void Refresh()
     public IEnumerator<Key> GetEnumerator()
     {
       var versionSnapshot = version;
-      var fetchedKeysBeforePersist = FetchedKeys;
-      var addedKeysBeforePersist = addedKeys;
-      var removedKeysBeforePersist = removedKeys;
-      foreach (var fetchedKey in fetchedKeysBeforePersist) {
-        if (versionSnapshot!=version)
-          throw new InvalidOperationException(Strings.ExCollectionHasBeenChanged);
-        if (!removedKeysBeforePersist.ContainsKey(fetchedKey))
-          yield return fetchedKey;
-      }
-      foreach (var addedKey in addedKeysBeforePersist) {
-        if (versionSnapshot!=version)
-          throw new InvalidOperationException(Strings.ExCollectionHasBeenChanged);
-        yield return addedKey.Value;
+      using (var fetchedKeysEnumerator = FetchedKeys.GetEnumerator()) {
+        while (true) {
+          if (versionSnapshot != version) {
+            throw new InvalidOperationException(Strings.ExCollectionHasBeenChanged);
+          }
+
+          if (!fetchedKeysEnumerator.MoveNext()) {
+            break;
+          }
+
+          var fetchedKey = fetchedKeysEnumerator.Current;
+          if (!removedKeys.ContainsKey(fetchedKey)) {
+            yield return fetchedKey;
+          }
+        }
       }
 
+      using (var addedKeysEnumerator = addedKeys.GetEnumerator()) {
+        while (true) {
+          if (versionSnapshot != version) {
+            throw new InvalidOperationException(Strings.ExCollectionHasBeenChanged);
+          }
+
+          if (!addedKeysEnumerator.MoveNext()) {
+            break;
+          }
+
+          var addedKey = addedKeysEnumerator.Current;
+          yield return addedKey.Value;
+        }
+      }
     }
 
     /// <inheritdoc/>