@Bean method metadata is always being picked from the most concrete subclass

As a side effect, @Bean overrides and overloads work with 'allowBeanDefinitionOverriding'=false as well now.

Issue: SPR-10992
Polishing (along with SPR-10992)
Only retrieve the FlashMapManager if a non-empty output FlashMap has been found

Issue: SPR-10937
(cherry picked from commit 4ac6801)
Perform setParent's Environment merging for ClassPathXmlApplicationContext etc constructors with parent argument as well

Issue: SPR-11068
(cherry picked from commit c5fcf19)
Disable ext entities in SourceHttpMessageConverter

This change disables the processing of external entities in
SourceHttpMessageConverter by default and provides an option to enable
it if required.
Fix exception mock request builder

Issue: SPR-11043
Return 415 on bad request body content-type

Issue: SPR-10982
JndiObjectFactoryBean converts a "defaultObject" value to the expected type if necessary

Issue: SPR-11039
(cherry picked from commit 0aedd81)
Added test for placeholder in alias definition

Issue: SPR-11018
(cherry picked from commit e9a24da)
Update changelog
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