Handle SUPERtype reference

[Jamie Thompson]

Compile with Dotty 0.22.x

object SuperTypes

  class Bar
    final val bar = "Bar.bar"

  class Foo extends Bar
    object A
      def unapply(a: Any): Some[Foo.super.bar.type] = ???

    def foo =
      "" match
        case A(x) => x // SUPERtype