Generate light classes for Kotlin inner classes

#KT-6237 Fixed

idea/testData/findUsages/kotlin/findFunctionUsages/kotlinNestedClassMethodUsages.0.kt

@@ -0,0 +1,11 @@
+// PSI_ELEMENT: org.jetbrains.jet.lang.psi.JetNamedFunction
+// OPTIONS: usages
+package a
+
+public open class Outer() {
+    open class Inner {
+        fun <caret>foo() {
+
+        }
+    }
+}