JS: move more test to box tests

js/js.translator/testData/box/native/kt1519.kt

@@ -0,0 +1,19 @@
+package foo
+
+@native
+class Wow() {
+    val x: Int = noImpl
+    val y: Int = noImpl
+}
+
+@native
+fun Wow.sum(): Int = noImpl
+
+fun Wow.dblSum(): Int {
+    return 2 * sum()
+}
+
+
+fun box(): String {
+    return if (Wow().dblSum() == 6) "OK" else "fail"
+}