JIRA: https://jira.spring.io/browse/INT-4456
Since Kotlin compiles lambdas different way than Java, they are not
synthetic classes at runtime anymore.
Therefore we fallback to the method invocation logic, but since Java 8
interfaces has `default` methods as well the `MessagingMethodInvokerHelper`
can't select the target method for invocation
* Use explicit `Function.apply()` for non-synthetic implementations
* Add `RouterDslTests` Kotlin-based test-case
**Cherry-pick to 5.0.x**
* Add more explicit methods for invokers
0c1423e78a