KT-43941 [Sealed interfaces]: subclass intention

Restriction for sealed inheritors was relaxed. Instead of being nested
class members now they can be the members of the same module and
package.

idea/testData/quickfix/implement/sealedAfter15.kt

@@ -0,0 +1,8 @@
+// "Implement sealed class" "true"
+// WITH_RUNTIME
+// SHOULD_BE_AVAILABLE_AFTER_EXECUTION
+// COMPILER_ARGUMENTS: -XXLanguage:+SealedInterfaces
+
+sealed class <caret>Base {
+    abstract fun foo(): Int
+}