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.
This is way too immutable.
It will not be modified if the project was updated to the next version of Scala in the source repository (with the project preferences shared), or if the user updates its Scala IDE installation with a new version of Scala.