KJS: introduce new base class WebDemoExamples* tests

js/js.translator/testData/webDemoExamples1/patternMatching.kt

@@ -0,0 +1,18 @@
+fun main(args: Array<String>) {
+    cases("Hello")
+    cases(1)
+    cases(MyClass())
+    cases("hello")
+}
+
+fun cases(obj: Any) {
+    when(obj) {
+        1 -> println("One")
+        "Hello" -> println("Greeting")
+        !is String -> println("Not a string")
+        else -> println("Unknown")
+    }
+}
+
+class MyClass() {
+}