Ensure Parent ConfigurationClass loaded on overrides

Previously ConfigurationClassParser could override a nested
@Configuration without consideration of @Bean's defined in parent
classes.

This commit ensures that if the original ConfigurationClass contains
additional bean definitions it is processed again.

Issue: SPR-10546
(cherry picked from commit 940011e)
Properly handle knownSuperclasses in case of an overridden ConfigurationClass

Issue: SPR-10546
(cherry picked from commit 6e4317e)
Fixed type detection to avoid reuse of parent bean's targetType on child definition merge

Issue: SPR-10374
Polishing
Avoid unnecessary creation of default StandardEnvironment instances

Issue: SPR-10568
Introduced "jsonPrefix" bean property

This change involves a modification of the "writeContent" template method to include the "jsonPrefix" String instead of the "prefixJson" boolean flag. Since said template method has only been introduced in 3.2.2, this change should hopefully not be a problem.

Issue: SPR-10567
Fix bug with deriving SockJS path