Related to https://stackoverflow.com/questions/75109345/spring-integration-webflux-inboundgateway-replychannel-for-error-response
The `MessagingGatewaySupport.doSendAndReceiveMessageReactive()` uses `MutableMessageBuilder`
to build a new message for next `send` operation.
Even if this is an error flow, the provided `ErrorMessage` becomes a plain `MutableMessage`.
This may break some downstream logics, like `TracingChannelInterceptor` from Spring Cloud Sleuth,
which checks for the `Message` class to rebuild or reuse a message content.
Therefore, an error handling flow is not able to extract error info because it is just lost.
* Fix `MessagingGatewaySupport.doSendAndReceiveMessageReactive()` to check for message type before
choosing an `AbstractIntegrationMessageBuilder` impl for building a new message.
The regular `MessageBuilder` just builds a new `ErrorMessage` for an exception payload.
* Add `filter()` into a `WebFluxDslTests` error handling flow to be sure that message for
error sub-flow is really an `ErrorMessage`
a1f57e40cd