* Make use of `TYPESAFE_PROJECT_ACCESSORS` and `VERSION_CATALOGS` Gradle feature previews to clean up build scripts
* Bump setup-java action to v2, specify AdoptOpenJDK distribution
This has been tested on the following:
- AdoptOpenJDK Java 1.8.0_282
- GraalVM CE 21.0.0 OpenJDK 11.0.10
- AdoptOpenJDK Java 15.0.2
- AdoptOpenJDK Java 16 (also tested with BungeeCord b1556)
- Amazon Corretto OpenJDK 16.0.0.36.1
... with Waterfall b406 on Linux 5.10.28.
This does not affect any previous states of this project; only future modifications as well as the project as a whole will be under the GNU General Public License from now on. The newly introduced api directory, partly split from common, is an exception to this, still being licensed under the MIT license.
See the README for details.
