Optimize `List.from`
Optimize `List.from`

If the source collection is already a `ListBuffer`, there is no need
to copy it. We can just publish it as a `List`.

scala/scala,lrytz/scala,scala/scala,martijnhoekstra/scala,martijnhoekstra/scala,lrytz/scala,martijnhoekstra/scala,martijnhoekstra/scala,lrytz/scala,scala/scala,martijnhoekstra/scala,martijnhoekstra/scala,scala/scala,lrytz/scala,scala/scala,lrytz/scala,scala/scala,lrytz/scala