Move all public Java classes to libreoffice.jar

This moves the classes from juh.jar and ridl.jar to libreoffice.jar

The goal is to have one single jar (and Java module, will be added later)
which developers can include to work with LO.

juh.jar and ridl.jar are kept as basically empty jars with libreoffice.jar
on its classpath to keep backwards compatibility.

This is a continuation of ae855bf48163ff64d94cfc34aff8e37abdb5518d
and a preparation to have Java 9 module support.

Change-Id: Ifbbfb97f60373d14256e62ae3122913bd17d5bbb
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/91930
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>