WebSocket messaging's task executors are only auto-configured and stompWebSocketHandlerMapping is only forced to be eager when using Jackson

[wilkinsona]

The conditions that are used and the structure of WebSocketMessagingAutoConfiguration and its inner classes are such that we lose some configuration in the absence of Jackson. The configuration that's lost is:

• the inbound and outbound channels' executors
• the bean that forces the stompWebSocketHandlerMapping bean to be eager when lazy init is enabled