Synchronization for updatable entity views within nested transaction doesn't work

[beikov]

The SynchronizationRegistry associates one Synchronization (i.e. itself) with a transaction through the current thread, but since a transaction can be suspended to create a new one, this results in trouble, because nested transactions don't get a Synchronization registered. Ultimately, this leads to post-commit listeners not being triggered when a nested transaction commits, but rather when the parent transaction to which the SynchronizationRegistry was associated commits.