[FE] Prohibit inheritance of sealed classes in different module

KT-20423

compiler/testData/diagnostics/tests/sealed/inheritorInDifferentModule.kt

@@ -0,0 +1,17 @@
+// ISSUE: KT-20423
+// !LANGUAGE: +SealedInterfaces +FreedomForSealedClasses
+
+// MODULE: m1
+// FILE: a.kt
+package a
+
+sealed class Base
+
+class A : Base()
+
+// MODULE: m2(m1)
+// FILE: b.kt
+
+package a
+
+class B : <!INVISIBLE_MEMBER, SEALED_INHERITOR_IN_DIFFERENT_MODULE!>Base<!>()