DEV: Extensively use includes() (#17541)

Also, the change in insert-hyperlink (from `this.linkUrl.indexOf("http") === -1` to `!this.linkUrl.startsWith("http")`) was intentional fix: we don't want to prevent users from looking up topics with http in their titles.

app/assets/javascripts/admin/addon/controllers/admin-web-hooks-show-events.js

@@ -38,7 +38,7 @@ export default Controller.extend({
   _addIncoming(eventId) {
     const incomingEventIds = this.incomingEventIds;
 
-    if (incomingEventIds.indexOf(eventId) === -1) {
+    if (!incomingEventIds.includes(eventId)) {
       incomingEventIds.pushObject(eventId);
     }
   },