feat(HttpClient): add JSON.stringify replacer

Adds optional parameter for replacer to be used when stringifying json.

src/util.js

@@ -3,8 +3,9 @@
 * Useful for easily creating JSON fetch request bodies.
 *
 * @param body The object to be serialized to JSON.
+* @param replacer The JSON.stringify replacer used when serializing.
 * @returns A Blob containing the JSON serialized body.
 */
-export function json(body: any): Blob {
-  return new Blob([JSON.stringify((body !== undefined ? body : {}))], { type: 'application/json' });
+export function json(body: any, replacer?: any): Blob {
+  return new Blob([JSON.stringify((body !== undefined ? body : {}), replacer)], { type: 'application/json' });
 }