Refactor js.tests

Use Test#getName where possible

js/js.translator/testFiles/operatorOverloading/cases/postfixInc.kt

@@ -0,0 +1,18 @@
+package foo
+
+class MyInt() {
+  var b = 0
+
+    fun inc() : MyInt {
+        val res = MyInt()
+        res.b++;
+        return res;
+    }
+}
+
+
+fun box() : Boolean {
+    var c = MyInt()
+    c++;
+    return (c.b == 1);
+}