DEV: enforces ember-template-lint: no-triple-curlies (#9150)

This pr replaces `{{{ }}}` usage by a {{html-safe}} helper. While it doesn't solve the underlying issue, it gives us a path forward without risking breaking too much existing behavior.

Also introduces an htmlSafe computed macro:

```
import { htmlSafe } from "discourse/lib/computed";

htmlDescription: htmlSafe("description")
```

Overtime {{html-safe}} usage should be removed and moved to components properties or specialized components/helpers.

lib/onebox/templates/discourse_topic_onebox.hbs

@@ -1,10 +1,10 @@
 <aside class='quote' data-post="{{post_number}}" data-topic="{{topic_id}}">
   <div class='title'>
     <div class='quote-controls'></div>
-    {{{avatar}}}
-    <a href="{{original_url}}">{{{title}}}</a> {{{category_html}}}
+    {{html-safe avatar}}
+    <a href="{{original_url}}">{{html-safe title}}</a> {{html-safe category_html}}
   </div>
   <blockquote>
-    {{{quote}}}
+    {{html-safe quote}}
   </blockquote>
 </aside>

lib/onebox/templates/discourse_user_onebox.hbs

@@ -1,7 +1,7 @@
 <aside class="onebox">
   <article class="onebox-body user-onebox">
-    {{{avatar}}}
-    <h3><a href="{{original_url}}">{{{username}}}</a></h3>
+    {{html-safe avatar}}
+    <h3><a href="{{original_url}}">{{html-safe username}}</a></h3>
     <div>
       {{#name}}
         <span class="full-name">{{name}}</span>
@@ -11,7 +11,7 @@
           <svg class="fa d-icon d-icon-map-marker-alt svg-icon" xmlns="http://www.w3.org/2000/svg">
             <use xlink:href="#map-marker-alt"></use>
           </svg>
-          {{{location}}}
+          {{html-safe location}}
         </span>
       {{/location}}
       {{#website}}
@@ -19,12 +19,12 @@
           <svg class="fa d-icon d-icon-globe-americas svg-icon" xmlns="http://www.w3.org/2000/svg">
             <use xlink:href="#globe-americas"></use>
           </svg>
-          <a href="{{website}}">{{{website_name}}}</a>
+          <a href="{{website}}">{{html-safe website_name}}</a>
         </span>
       {{/website}}
     </div>
     {{#bio}}
-      <p>{{{bio}}}</p>
+      <p>{{html-safe bio}}</p>
     {{/bio}}
     <span>{{joined}} {{created_at}}</span>
   </article>