Adopt Scala example

Scala sbt-layout tree with a greet package and a stdlib-only solo package.

bazel run @rules_dx//:dx -- init //examples/adopt-scala/...
bazel run @rules_dx//:dx -- generate //examples/adopt-scala/...
bazel build //examples/adopt-scala/...
bazel test //examples/adopt-scala/...

Both tests pass (greet_test, pure_test).

For Scalafix lint, see docs/cli/commands/quality.md.