When a BiConsumer user function is provided, we wrap it inside a Function
when registering it in FunctionRegstration. FunctionInvocationWrapper sees
this as a Function and downstream clients (such as Spring Cloud Stream) does
not have visibility into the user function type from a FunctionInvocationWrapper
API perspective. This commit propagates the BiConsumer targer user function info
as part of FunctionInvocationWrapper API.
For more information, see: https://github.com/spring-cloud/spring-cloud-stream/issues/2670Resolves#1016