Match type pickling test failure

[OlivierBlanvillain]

The following fails to pass the pickling tests:

object Test {
  type M[X] = X match { case Int => String }
  def a: Any { type Out = M[Int] } = a
}

(minimized from #13585)

The failure comes from the refinement type, which is printed as
scala.Any{Out = scala.String} before pickling, and
scala.Any{Out = Test.M[scala.Int]} after pickling.

[dwijnand]

I think the change in #14506 affects this. Type simplifies and overrides the type. So not doing so in unpickling is going to make the tree have different types. We need to either continue to do it, or do it while comparing the types. (That PR post-dates this issue, so I think the simplify wasn't there initially, then it was there, then it was removed - so the issue is still present.)