SPR-11825 SubPWSocketH: eventPublisher population

JIRA: https://jira.spring.io/browse/SPR-11825

As long as `StompSubProtocolHandler` has been created directly in case of `@EnableWebSocketMessageBroker`,
there was no application context infrastructure population.

Make `WebMvcStompEndpointRegistry` as `ApplicationContextAware` and populate it to the
`StompSubProtocolHandler.setApplicationEventPublisher`

**Cherry-pick to 4.0.x**