Added delegated property through map support + tests.

backend.native/tests/codegen/delegatedProperty/observable.kt

@@ -0,0 +1,14 @@
+import kotlin.properties.Delegates
+
+class User {
+    var name: String by Delegates.observable("<no name>") {
+        prop, old, new ->
+        println("$old -> $new")
+    }
+}
+
+fun main(args: Array<String>) {
+    val user = User()
+    user.name = "first"
+    user.name = "second"
+}