PayloadArgumentResolver does not insist on configured Validator anymore

Issue: SPR-12567
AnnotationJmxAttributeSource uses AnnotationUtils for consistent meta-annotation handling and diagnostics

Issue: SPR-12572
Spring's JMX support can rely on native MXBean detection on Java 6+

Issue: SPR-12574
Doc: base-packages can be comma/semicolon/space/tab/linefeed-separated

Issue: SPR-12523