Scala Installations support

Adds a valid, persistent, best-effort scala library bundle setup on classpath after the choice of a scala desired source level in project-scopes compiler options.

Operates by modifying and serializing the scala classpath container.

Does not include scala-installation registry edition yet.
Why not just use Classpath resolution ?  We don't know in advance if this needs `scala-{library, compiler, ...}` jars, but the classpath's container resolution should be set up correctly, and tell us so implicitly.