Prior to this commit, the `WebSocketMessageBrokerStats` would be in
charge of periodically logging WebSocket stats. This class would also
publicly expose each stats type with dedicated methods, as `String`.
This would not allow observation libraries to easily extract information
and turn them into metrics.
This commit introduces new methods exposing the `Stats` types directly
and deprecates the former `String` variants. This will allow
observability libraries like Micrometer to expose this as metrics:
```
MeterRegistry meterRegistry = ...;
Gauge.builder("spring.stomp.frames", stats.getStompSubProtocolStats(),
StompSubProtocolHandler.Stats::getTotalConnect)
.tag("type", "CONNECT")
.description("number of CONNECT frames processed")
.register(meterRegistry);
```
Closes gh-31604
3b53165574