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.

public/javascripts/embed.js

@@ -81,7 +81,7 @@
     if (!e) {
       return;
     }
-    if (normalizeUrl(DE.discourseUrl).indexOf(normalizeUrl(e.origin)) === -1) {
+    if (!normalizeUrl(DE.discourseUrl).includes(normalizeUrl(e.origin))) {
       return;
     }