Add node querystring polyfill (#4370)

std/node/querystring_test.ts

@@ -0,0 +1,30 @@
+const { test } = Deno;
+import { assertEquals } from "../testing/asserts.ts";
+import { stringify, parse } from "./querystring.ts";
+
+test({
+  name: "stringify",
+  fn() {
+    assertEquals(
+      stringify({
+        a: "hello",
+        b: 5,
+        c: true,
+        d: ["foo", "bar"]
+      }),
+      "a=hello&b=5&c=true&d=foo&d=bar"
+    );
+  }
+});
+
+test({
+  name: "parse",
+  fn() {
+    assertEquals(parse("a=hello&b=5&c=true&d=foo&d=bar"), {
+      a: "hello",
+      b: "5",
+      c: "true",
+      d: ["foo", "bar"]
+    });
+  }
+});