[JS IR] Support per-file mode and ES modules

js/js.translator/testData/box/esModules/jsModule/externalClass.mjs

@@ -0,0 +1,11 @@
+export default function A(x) {
+    this.x = x;
+}
+
+A.prototype.foo = function (y) {
+    return this.x + y;
+};
+
+A.prototype.bar = function() {
+    return "(" + Array.prototype.join.call(arguments, "") + ")";
+};