address review

Use TypeBounds instead of WildcardType. WildcardType has the
following unexpected behavior:

    Array[?] <:< Array[Array[?]]

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -356,11 +356,8 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
 
     val map = new TypeMap {
       def apply(tp: Type) = tp match {
-        case tp @ AppliedType(tycon, args) if tycon.isRef(defn.ArrayClass) =>
-          // walkaround `Array[_] <:< Array[Array[_]]`, see tests/patmat/t2425.scala
-          tp.derivedAppliedType(tycon, args.map(mapOver))
         case tref: TypeRef if isPatternTypeSymbol(tref.typeSymbol) =>
-          WildcardType(tref.underlying.bounds)
+          tref.underlying.bounds
         case _ => mapOver(tp)
       }
     }