Remove T <: S and make S contravariant

Author: nicolasstucki

docs/docs/reference/other-new-features/type-test.md

@@ -10,7 +10,7 @@ TypeTest
 `TypeTest.unapply` will return `Some(x.asInstanceOf[Y])` if `x` conforms to `Y`, otherwise it returns `None`.
 
 ```scala
-trait TypeTest[S, T <: S] extends Serializable {
+trait TypeTest[-S, T] extends Serializable {
   def unapply(s: S): Option[s.type & T]
 }
 ```

library/src/scala/reflect/TypeTest.scala

@@ -1,6 +1,6 @@
 package scala.reflect
 
-/** A `TypeTest[S, T]` (where `T <: S`) contains the logic needed to know at runtime if a value of
+/** A `TypeTest[S, T] contains the logic needed to know at runtime if a value of
  *  type `S` can be downcased to `T`.
  *
  *  If a pattern match is performed on a term of type `s: S` that is uncheckable with `s.isInstanceOf[T]` and
@@ -12,7 +12,7 @@ package scala.reflect
  *  Note: This is replacemet for `ClassTag.unapply` that can be sound for path dependent types
  */
 @scala.annotation.implicitNotFound(msg = "No TypeTest available for [${S}, ${T}]")
-trait TypeTest[S, T <: S] extends Serializable {
+trait TypeTest[-S, T] extends Serializable {
 
   /** A TypeTest[S, T] can serve as an extractor that matches only S of type T.
    *