feat(d.ts): add createAnonymousContext & runInBackground (#2501)

index.d.ts

@@ -609,6 +609,22 @@ declare module 'egg' {
     Controller: Controller;
 
     middleware: KoaApplication.Middleware[] & IMiddleware;
+
+    /**
+     * Create an anonymous context, the context isn't request level, so the request is mocked.
+     * then you can use context level API like `ctx.service`
+     * @member {String} Application#createAnonymousContext
+     * @param {Request} req - if you want to mock request like querystring, you can pass an object to this function.
+     * @return {Context} context
+     */
+    createAnonymousContext(req?: Request): Context;
+
+    /**
+     * Run async function in the background
+     * @see Context#runInBackground
+     * @param {Function} scope - the first args is an anonymous ctx
+     */
+    runInBackground(scope: (ctx: Context) => void): void;
   }
 
   export interface FileStream extends Readable { // tslint:disable-line