Include Java 17 sources in multi-release jar #219
Description
While migrating to Multi-release jar in #214, the published version 1.1.0 only contains the source code for Java 11.
This is possible the issue in https://github.com/melix/mrjar-gradle-plugin plugin. Since it doesn't seem to be well supported and due to having other issues with dependencies, we might need to reimplement the support from scratch, using the plugin as a reference.
The source code needs to be included in META-INF/versions/17, just like with compiled jar.