Support sealed class inheritors in the same file

#KT-11573 Fixed

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

@@ -0,0 +1,9 @@
+class A {
+    sealed class Base
+}
+
+class Derived : <!INVISIBLE_MEMBER, SEALED_SUPERTYPE!>A.Base<!>()
+
+fun test() {
+    class DerivedLocal : <!INVISIBLE_MEMBER, SEALED_SUPERTYPE!>A.Base<!>()
+}