Changes

Move the build to require JDK 11

-update build plugins (allows building on Java SE 15),
-resurrect building temporarily excluded parts (#473),
-fix content of provider implementation files (#493)
-define missing JPMS descriptors and fix existing ones,
  move away from Automatic-Module-Name in manifests
-include JPMS descriptors in final jar filess

Signed-off-by: Lukas Jungmann <lukas.jungmann@oracle.com>
 (commit: b497ec0)