DEV: Introduce discourseLater (#17532)

A wrapper for `later()` from `@ember/runloop`, similar to `discourseDebounce`. It automatically reduces the delay in testing environment.

app/assets/javascripts/discourse-common/addon/lib/later.js

@@ -0,0 +1,14 @@
+import { later } from "@ember/runloop";
+import { isTesting } from "discourse-common/config/environment";
+
+export default function () {
+  if (isTesting() && typeof [...arguments].at(-1) === "number") {
+    // Replace the `wait` argument with 10ms
+    let args = [].slice.call(arguments, 0, -1);
+    args.push(10);
+
+    return later.apply(undefined, args);
+  } else {
+    return later(...arguments);
+  }
+}