Create subclass intention implemented #KT-8473 Fixed

Can be used for implementing interfaces / abstract classes / sealed classes or extending open classes

idea/testData/quickfix/implement/nestedPrivateInterface.kt

@@ -0,0 +1,8 @@
+// "Implement interface" "true"
+// SHOULD_BE_AVAILABLE_AFTER_EXECUTION
+
+class Container {
+    private interface <caret>Base {
+        var z: Double
+    }
+}