Fixed toFormData regression bug (unreleased) with Array-like objects serialization; (#4714)

Added `toURLEncodedForm` helper;
Added automatic payload serialization to `application/x-www-form-urlencoded` to have parity with `multipart/form-data`;
Added test of handling `application/x-www-form-urlencoded` body by express.js;
Updated README.md;
Added missed param in JSDoc;
Fixed hrefs in README.md;

Co-authored-by: Jay <jasonsaayman@gmail.com>

lib/platform/browser/classes/URLSearchParams.js

@@ -0,0 +1,38 @@
+'use strict';
+
+module.exports = (function getURLSearchParams(nativeURLSearchParams) {
+  if (typeof nativeURLSearchParams === 'function') return nativeURLSearchParams;
+
+  function encode(str) {
+    var charMap = {
+      '!': '%21',
+      "'": '%27',
+      '(': '%28',
+      ')': '%29',
+      '~': '%7E',
+      '%20': '+',
+      '%00': '\x00'
+    };
+    return encodeURIComponent(str).replace(/[!'\(\)~]|%20|%00/g, function replacer(match) {
+      return charMap[match];
+    });
+  }
+
+  function URLSearchParams() {
+    this.pairs = [];
+  }
+
+  var prototype = URLSearchParams.prototype;
+
+  prototype.append = function append(name, value) {
+    this.pairs.push([name, value]);
+  };
+
+  prototype.toString = function toString() {
+    return this.pairs.map(function each(pair) {
+      return pair[0] + '=' + encode(pair[1]);
+    }, '').join('&');
+  };
+
+  return URLSearchParams;
+})(URLSearchParams);