Also compute base classes of wildcardTypes

Fixes #19460

[Cherry-picked 725c425]

Author: odersky

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

@@ -640,6 +640,8 @@ object Types extends TypeUtils {
             tp.superType.baseClasses
           case tp: ClassInfo =>
             tp.cls.classDenot.baseClasses
+          case tp: WildcardType =>
+            tp.effectiveBounds.hi.baseClasses
           case _ => Nil
       catch case ex: Throwable =>
         handleRecursive("base classes of", this.show, ex)

tests/pos/i19460.scala

@@ -0,0 +1,5 @@
+type T[A] = A | Any
+
+def perform[A](using T[A]): A = perform2
+
+def perform2[A](using T[A]): A = ???