java/junit: 4.11 -> 4.12

Changes:
https://github.com/junit-team/junit/blob/master/doc/ReleaseNotes4.12.md

Moved from building from source with ant to using the binary jar file,
as the new build mechanism is based on maven. java/hamcrest was split
from 4.12.

PR: 192575
Submitted by: danilo (maintainer), kevin.bowling@kev009.com