Merge branch '6.0' into 7.0

# Conflicts:
#	Version.props

Author: alex-kulakov

Extensions/Xtensive.Orm.BulkOperations/Internals/Operation.cs

@@ -50,7 +50,15 @@ public async Task<int> ExecuteAsync(CancellationToken token = default)
       return value;
     }
 
-    protected void EnsureTransactionIsStarted() => Transaction.Require(QueryProvider.Session);
+    protected void EnsureTransactionIsStarted()
+    {
+      Transaction.Require(QueryProvider.Session);
+#pragma warning disable 168
+      // this prepares connection which ensures that connection is opened
+      // this is weird way but it is required for some scenarios.
+      _ = QueryProvider.Session.Services.Demand<DirectSqlAccessor>().Transaction;
+#pragma warning restore 168
+    }
 
     protected abstract int ExecuteInternal();