Added tests on class delegation

backend.native/tests/codegen/classDelegation/generic.kt

@@ -0,0 +1,21 @@
+open class Content() {
+    override fun toString() = "OK"
+}
+
+interface Box<E> {
+    fun get(): E
+}
+
+interface ContentBox<T : Content> : Box<T>
+
+object Impl : ContentBox<Content> {
+    override fun get(): Content = Content()
+}
+
+class ContentBoxDelegate<T : Content>() : ContentBox<T> by (Impl as ContentBox<T>)
+
+fun box() = ContentBoxDelegate<Content>().get().toString()
+
+fun main(args: Array<String>) {
+    println(box())
+}