JS: move expressions test to box tests

js/js.translator/testData/box/expression/invoke/invokeMethod.kt

@@ -0,0 +1,13 @@
+package foo
+
+class Foo(val postfix: String) {
+    operator fun invoke(text: String): String {
+        return text + postfix
+    }
+}
+
+fun box(): String {
+    val a = Foo(" world!")
+    assertEquals("hello world!", a("hello"))
+    return "OK"
+}