* Include Scala 3 in cross-build
sbt cross-building sometimes behaves surprisingly, so this does not work
yet: when switching to 3.0.1-RC1 it still tries to build the modules
that do not support that version yet, even though they are 'excluded'.
This also currently breaks cross-publishing, so we cannot merge this.
Once this works we should add a note to the documentation clarifying
that the Scala 3 artifacts are experimental.
* Fix jackson test dependency
* Don't publish docs for scala3 artifacts for now
* Publish empty doc packages for Scala 3 artifacts
This should have been implicit with the -release flag, and now
this indeed appears to be the case. Tested with 2.12 and 2.13.0
Fixes the scalac part of #27079
