URL params serializer; (#4734)

* Refactored BuildURL helper to use URLSearchParams serializer;

* Updated typings;
Added TS test;

lib/helpers/toFormData.js

@@ -46,6 +46,10 @@ function isSpecCompliant(thing) {
  **/
 
 function toFormData(obj, formData, options) {
+  if (!utils.isObject(obj)) {
+    throw new TypeError('target must be an object');
+  }
+
   // eslint-disable-next-line no-param-reassign
   formData = formData || new (envFormData || FormData)();