Add JPMS module-info.java

I'm not sure that anyone will ever need this. But I mistakenly thought that we did to reproduce a user bug, so I started experimenting in the `feat/module-info` branch ([see diff](https://github.com/diffplug/selfie/compare/main...feat/module-info)).

The hiccups I ran into were:

- the `module-info.java` has to be in a `java` folder, not a `kotlin` folder
- stuff that is in the `java` folder can't reference stuff in the `kotlin` folder
- we needed fake package-private `NeededForModuleInfo.java` files in the java folder to avoid compilation errors in the `module-info.java`

If you need selfie to support `module-info.java`, I'm happy to merge a PR that does it, and you can use this as a starting point.

- the hiccups above are fine with me. If you can fix the workarounds great, but I don't mind shipping them
- please merge in from main first, maybe the latest version of the Kotlin plugin will have made it easier by then
- I would like the metadata (naming and whatsuch) to be canonical, and I don't have enough experience with JPMS to know what it should be. Hopefully if you need JPMS, you've also got enough experience that you can set this metadata better than I did.

Beginne mit der Überprüfung des Diffs des Branches feat/module-info und dem Zusammenführen des aktuellen main, und untersuche anschließend dessen module-info.java sowie die unechten NeededForModuleInfo.java-Dateien im java-Ordner. Bestätige die kanonischen JPMS-Metadaten bei den Projekt-Maintainern oder in der JPMS-Dokumentation. Erledigt ist die Aufgabe, wenn selfie module-info.java mit den erforderlichen Dateien unterstützt, die erfolgreich kompiliert werden.

Vom Indexierungsmodell aus dem Issue-Text verfasst.