Implement Kotlin Script support in UAST

#KT-18353 Fixed

plugins/uast-kotlin/testData/InnerClasses.kt

@@ -0,0 +1,8 @@
+class Foo {
+    class Bar(val a: Int, val b: Int) {
+        fun getAPlusB() = a + b
+        class Baz {
+            fun doNothing() = Unit
+        }
+    }
+}