AMQP-451 Batching RabbitTemplate

JIRA: https://jira.spring.io/browse/AMQP-451

Released in stealth mode for now (no docs, javadocs marked `Experimental`).

This feature is to support XD; we can't incubate in XD because it needs a
change to the listener container.

AMQP-451 Add Perf Test

Move Debatching Code

Move from `SMLC.doReceiveAndExecute()` to `AMLC.executeListener()`.

- Change the cause of the `ListenerExecutionFailedException` on a bad
decode to a `MessageConversionException` so that the default error handler
will cause the message to be rejected - otherwise the badly formed message
will continually be redelivered by default.
- Add a test case to ensure a badly formed message is rejected.