DefaultListableBeanFactory defensively handles BeanDefinition access in getBean(Class)

Issue: SPR-10542
(cherry picked from commit 9d3d6d5)
PersistenceAnnotationBeanPostProcessor defensively handles BeanDefinition access for extended EntityManagers

Issue: SPR-8834
(cherry picked from commit 592e344)
DispatcherServlet's checkMultipart detects wrapped MultipartRequest as well

Issue: SPR-12114
(cherry picked from commit 786fd92)
Consistent attribute documentation/formatting in spring-context and spring-mvc schemas
(cherry picked from commit b5763fe)
PropertySource implementations perform conversion to String arrays via StringUtils (getting rid of EMPTY_NAMES_ARRAY)
(cherry picked from commit b73c531)
Polishing
Include ALL source artifacts in published sources jars

This commit updates the Gradle build to ensure that *all* source
artifacts are including in published 'sources' jars.

To achieve this, we are now assembling 'sources' jars from
'sourceSets.main.allSource' and not explicitly including or excluding
anything by default.

Issue: SPR-12085
(cherry picked from commit 07629a3c7cc9ad677d31d383015410ad3395addc)