Previously, the `@Order` annotation was managed in an inconsistent way
when placed at the implementation level. For simple beans, it was
discovered properly but wasn't for beans requiring a proxy.
OrderComparator.SourceProvider now explicitly allows to return several
order sources; the default implementation returns not only the factory
method (if any) but also the target class if it happens to be different
from the class of the bean.
Issue: SPR-12636
1aec6a6cc2