Refined DefaultJpaDialect's InvalidIsolationLevelException message

Issue: SPR-8325
(cherry picked from commit af13310)
Reference documentation backports

Issue: SPR-11944
Issue: SPR-11945
Jms2MessageProducerInvocationHandler properly delegates to CachedMessageProducer.this

Issue: SPR-11949
(cherry picked from commit 134e5a2)
Jms2MessageProducerInvocationHandler specifically delegates all CompletionListener-based send methods

Issue: SPR-11950
(cherry picked from commit b6a7957)