JS: add tests for reflection against external classes

js/js.translator/testData/box/reflection/external.js

@@ -0,0 +1,4 @@
+function A() {
+}
+
+var O = {};

js/js.translator/testData/box/reflection/external.kt

@@ -0,0 +1,13 @@
+external class A
+
+external object O
+
+fun box(): String {
+    assertEquals(null, A::class.simpleName, "simpleName of external class must be null")
+    assertEquals(js("A"), A::class.js, "Can't get reference to external class")
+
+    assertEquals(null, O::class.simpleName, "simpleName of external object must be null")
+    assertEquals(js("O"), O::class.js, "Can't get reference to external object via instance")
+
+    return "OK"
+}