Spring Optimize DefaultLifecycleProcessor::stopBeans

Optimize DefaultLifecycleProcessor by reducing sorting and refactor stopBeans method.

Do this change due to LifecycleGroup has been sorted and member in which has same phase, so resort LifecycleGroupMember list to be meaningless.

If any improvements can do, feel free to tell me.

Comment From: simonbasle

LGTM. I've added some polish to the javadoc since it was making references to Comparable nature.