Unsubscribe from 1..n topic(s) in multi-topic/regexp subscription

Is there a way to unsubscribe from some topics in multi-topics subscription?

```go
consumer, err := pulsarClient.Subscribe(pulsar.ConsumerOptions{
Topics: []string{"topic1", "topic2", "topic3"},
// TopicsPattern: "topic*",
SubscriptionName: "test-subscription",
Type: pulsar.Shared,
SubscriptionInitialPosition: pulsar.SubscriptionPositionEarliest,
})

// TODO
consumer.UnsubscribeTopic("topic1","topic2")
consumer.CloseTopic("topic1", "topic2")
```

Start by tracing the Consumer returned by Subscribe with multiple Topics or a TopicsPattern, then examine the proposed consumer.UnsubscribeTopic and consumer.CloseTopic entry points. Determine the expected behavior when selected topics are removed while others remain; done means the issue's requested selective unsubscribe or close behavior is defined and verified without disrupting the remaining subscription.

Written by the indexing model from the issue text.