KJS: introduce new base class WebDemoExamples* tests

js/js.translator/testData/webDemoExamples1/forLoop.kt

@@ -0,0 +1,9 @@
+fun main(args: Array<String>) {
+    for (arg in args)
+        println(arg)
+
+    // or
+    println()
+    for (i in args.indices)
+        println(args[i])
+}