[FE] Always infer upper types to intersection types in K2...

...and always use old algorithm for K1

^KT-51221

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -902,6 +902,9 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         return this is UnwrappedType && constructor is NewTypeVariableConstructor
     }
 
+    override val isK2: Boolean
+        get() = false
+
     class WA // Workaround for KT-52313
 }