This commit fixes Javadoc generation when building with Java 9. It
upgrades the Javadoc plugin to a version that is Java 9 compatible
(3.0.0-M1) and reworks DevTools to remove usage of @PostConstruct.
The latter change is necessary as @PostConstruct is not visible by
default when building with Java 9 and, therefore its usage causes
Javadoc generation to fail.

Closes gh-10029