Don't warn if methods annotated @PreDestroy / @PostConstruct are unused

[kriths]

Methods annotated with @PreDestroy and @PostConstruct are managed by Java EE and the Java spec describes "The method [...] MAY be public, protected, package private or private". So I'd argue there shouldn't be are warning for private methods annotated with either of those annotations.

Those two annotations were also mentioned in #1235

See:
https://docs.oracle.com/javase/8/docs/api/javax/annotation/PostConstruct.html
https://docs.oracle.com/javase/8/docs/api/javax/annotation/PreDestroy.html

[eaftan]

Thanks for the contribution. By approving this, this PR will get transformed into an internal commit and then pushed back out, closing this PR. Please be patient while this happens.