Always include the local worker in the list of filtered targets.

It is currently legal to specify a device filter that doesn't include the local worker.
In that case, the MasterSession includes all local devices regardless of the filter.
This change extends this behavior to the list of filtered workers, which will be crucial for backwards compatibility when we enable CreateWorkerSession for all MasterSessions, because we need to call CreateWorkerSession on all potential workers.

PiperOrigin-RevId: 193613313