opaque type aliases broken in Worksheets

[bishabosha]

In 0.15.0-RC1 the type Foo can't be found within the Foo object in worksheet mode.

opaque type Foo = String

object Foo {
  def apply(s: String): Foo = s
}

[smarter]

Let's wait for #6567 to be done before investigating since it might solve end up solving this.

[bishabosha]

This is now redundant as it looks like opaque types are not allowed at the top level in a worksheet