Defer setting of PubSubChannelRegistry

Defer setting of PubSubChannelRegistry until afterPropertiesSet to ensure that all PubSubChannelRegistryAware handlers have been registered before the processing's performed.

Without this change, configuration like this:

```
<bean id="input-message-handler" class="org.springframework.web.messaging.service.method.AnnotationPubSubMessageHandler">
	<property name="pubSubChannelRegistry" ref="pubSubChannelRegistry"/>
</bean>
```

won't work as the PubSubChannelRegistryAware handlers aren't available when the PubSubChannelRegistry is passed down into ArgumentResolverComposite and ReturnValueHandlerComposite