Add module exception to allow viewing Javadoc in the SDK

[tonihele]

Add module exception to allow viewing Javadoc in the SDK. Seems that the following is needed:
-J--add-opens=java.base/java.io=ALL-UNNAMED
-J--add-opens=java.base/java.lang=ALL-UNNAMED

See:
https://hub.jmonkeyengine.org/t/ide-accessing-documentation-is-not-working/47704