Refined DefaultJpaDialect's InvalidIsolationLevelException message

Issue: SPR-8325
Reference documentation covers application scope now

Issue: SPR-11944
Jms2MessageProducerInvocationHandler properly delegates to CachedMessageProducer.this

Issue: SPR-11949
Add support for extra MessageProducer method

This commit supports two additional methods of the MessageProducer
interface as from JMS 2.0

An integration test infrastructure is necessary to be able to test
those scenario: this is taken care of in a separated initiative.

Issue: SPR-11950
Revised Jms2MessageProducerInvocationHandler implementation with switch statement

Issue: SPR-11950
Introduce tests for Spring Boot issue 885

This commit introduces unit tests that attempt to reproduce the problem
described in Spring Boot issue 885; however, the tests pass and
therefore do not confirm the reported problem.

See: https://github.com/spring-projects/spring-boot/issues/885