Make transluctentSuperType handle match types

This fixes several erasure related things, such as signature, or erasure itself.

Fixes #8666

Author: odersky

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -4011,7 +4011,7 @@ object Types {
       case tycon: TypeRef if tycon.symbol.isOpaqueAlias =>
         tycon.translucentSuperType.applyIfParameterized(args)
       case _ =>
-        superType
+        tryNormalize.orElse(superType)
     }
 
     inline def map(inline op: Type => Type)(using Context) =

tests/pos/i8666.scala

@@ -0,0 +1,10 @@
+class Foo[A, B]()
+
+type FooSnd[X] = X match
+  case Foo[_, b] => b
+
+trait Bar[A]:
+  def bar(h: FooSnd[A]): Int
+
+val foo: Bar[Foo[String, Int]] = new Bar[Foo[String, Int]]:
+  def bar(h: FooSnd[Foo[String, Int]]) = h