[JS TESTS] Rewrite web demo tests using new test infrastructure

js/js.translator/testData/webDemoExamples/multiLanguageHello.kt

@@ -0,0 +1,11 @@
+// MAIN_ARGS: [FR]
+
+fun main(args: Array<String>) {
+    val language = if (args.size == 0) "EN" else args[0]
+    println(when (language) {
+                "EN" -> "Hello!"
+                "FR" -> "Salut!"
+                "IT" -> "Ciao!"
+                else -> "Sorry, I can't greet you in $language yet"
+            })
+}