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

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

@@ -0,0 +1,9 @@
+export default function A(ss) {
+    this.s = ss || "A"
+}
+A.prototype.foo = function (y) {
+    return y || "K";
+};
+A.prototype.bar = function (y) {
+    return y || "O";
+};