Rework the reference documentation to better distinguish the differences
between @Bean methods used in @Comonent vs @Configuration classes. The
'Using the @Bean annotation' section now only covers concepts applicable
when using @Bean methods in @Configuration _or_ @Component classes.
Information only applicable to @Configuration classes has been moved to
a new 'Using the @Configuration annotation' section.
An additional sidebar section attempts to explain the differences
between the two approaches.
Issue: SPR-9425
Phillip Webb
5730b8d316