Now that responder RSocketStrategies also exposes responder strategies,
AnnotationClientResponderConfigurer is reduced and no longer needs to
be public. This commit folds it into RSocketMessageHandler as a nested
class and exposes it as a ClientRSocketFactoryConfigurer through a
static method that accepts the handlers to use.
Effectively a shortcut for creating RSocketMessageHandler, giving it
RSocketStrategies, calling afterPropertiesSet, and then the instance
createResponder.
See gh-23314
e19e36ae4c