existential subtyping confuses typevars created by withTypeVars and others

[adriaanm]

object Test extends App {
  class X[T]
  // expose bug with subtyping on existential types (in withTypeVars) with type params in their bounds
  def overloaded[T](b: X[T]) = println("Selected correct overload")
  def overloaded[T](b: X[_ <: T])(implicit bla: String = null) = ???
  overloaded(new X[String])
}

[adriaanm]

currently, this would be considered ambiguous. In scala/scala3#6230 there's a more elaborate example where the wrong overload is selected. It should be the first one (in both examples).