Migrate to MPS 2023.2

[alexanderpann]

• There was a change in the declaration of stub models. See: https://youtrack.jetbrains.com/issue/MPS-36814/Update-documentation-about-solution-settings-for-stubs
• The tests now run as JUnit5 tests. See: https://www.baeldung.com/junit-5-migration
• Runtime modules also have to be declared correctly or you will get ClassNotFoundExceptions when executing tests out-of-process.
• To avoid MPS-25087 which is the issues where icons are not showing up in actions which results in MPS-36726 and makes even main menu entries crash, the fix in Copy resources in the build script to make icons work again mbeddr/mps-qa#24 must be applied to all projects that this repository depends on.