Fix for KT-7421: Unable to inherit from inner class

Fix for KT-6708: Compiler Error when extending open inner class: "java.lang.RuntimeException: Error generating primary constructor of class InnerB with kind IMPLEMENTATION"

  #KT-7421 Fixed
  #KT-6708 Fixed

compiler/testData/codegen/box/classes/inner/kt6708.kt

@@ -0,0 +1,12 @@
+open class A() {
+    open inner class InnerA
+}
+
+class B : A() {
+    inner class InnerB : A.InnerA()
+}
+
+fun box(): String {
+    B().InnerB()
+    return "OK"
+}