Publish unidoc as ScalaDoc in chisel project (backport #2595) (#2597)

* Publish unidoc as ScalaDoc in chisel project (#2595)

This makes it such that we can stop hosting ScalaDoc on the Chisel
website, instead just pointing to the latest docs on javadoc.io

(cherry picked from commit 8b9f3d78

)

# Conflicts:
#	build.sbt

* Resolve backport conflicts

Co-authored-by: Jack Koenig <koenig@sifive.com>