FIX: uses tippy for popover (#15409)

Note this commit also introduce a new {{d-popover}} component, example usage:

```hbs
{{#d-popover |state|}}
  {{d-button label="foo.things" class="d-popover-trigger"}}

  <div class="d-popover-content">
    Some content
  <div>
{{/d-popover}}
```

vendor/assets/svg-icons/discourse-additional.svg

@@ -35,4 +35,9 @@ Additional SVG icons
   <symbol id="discourse-emojis" viewBox="0 0 216.3 152.3">
     <path d="M121.1 70.7c1.9 2 5.1 2.1 7.2.2l.2-.2 31.2-32.2c9.1-9.4 8.6-24.9-1.6-33.5-8.8-7.5-22-6.2-30.1 2.2l-3.2 3.3-3.2-3.3c-8.1-8.4-21.3-9.7-30.1-2.2-10.1 8.6-10.7 24.2-1.6 33.5l31.2 32.2zM53.5 45.3C23.9 45.3 0 69.2 0 98.8s23.9 53.5 53.5 53.5 53.5-24 53.5-53.5-23.9-53.5-53.5-53.5zm18.8 24.6c5.5 0 9.9 4.4 9.9 9.9s-4.4 9.9-9.9 9.9-9.9-4.4-9.9-9.9c-.1-5.5 4.4-9.9 9.9-9.9zm-38.2 0c5.5 0 9.9 4.4 9.9 9.9s-4.4 9.9-9.9 9.9-9.9-4.4-9.9-9.9 4.4-9.9 9.9-9.9zm52.4 45.4c-8.2 9.8-20.2 15.5-33.1 15.5s-24.9-5.6-33.1-15.5c-3.9-4.7 3.2-10.6 7.1-5.9 6.5 7.7 15.9 12.2 26 12.2s19.5-4.4 26-12.2c3.8-4.7 10.9 1.2 7.1 5.9zm129.8-22.5c0-6.4-6.3-9.5-13.3-9.5h-24c1.5-6 10.3-13.8 10.3-22.8 0-15.5-10.1-17.2-15.2-17.2-4.3 0-6.2 8.3-7.2 12.2-1.1 4.6-2.2 9.3-5.4 12.4-6.7 6.8-10.3 15.3-18.4 23.5-.7-1.8-2.6-3.1-4.7-3.1h-10.7c-2.8 0-5.1 2.2-5.1 4.9V142c0 2.7 2.3 4.9 5.1 4.9h10.7c2.8 0 5.1-2.2 5.1-4.9v-.9c.3.1.6.2.9.2 3.3.1 7.8 1.9 11.1 3.4 6.7 3 15.1 6.7 25.3 6.7h.6c9 0 19.7-.1 24-6.3 1.8-2.5 2.7-4.4.5-9.9 5-3 7-10 1-15 8-5 8-13 1-17 6.1-1.9 8.5-6.6 8.4-10.4z"></path>
   </symbol>
+  <!-- Rounded svg arrow for tippy.js, allows to change border color -->
+  <symbol id="tippy-rounded-arrow" class="tippy-rounded-arrow" viewBox="0 0 16 6">
+    <path class="svg-arrow" d="M0 6s1.796-.013 4.67-3.615C5.851.9 6.93.006 8 0c1.07-.006 2.148.887 3.343 2.385C14.233 6.005 16 6 16 6H0z"/>
+    <path class="svg-content" d="m0 7s2 0 5-4c1-1 2-2 3-2 1 0 2 1 3 2 3 4 5 4 5 4h-16z"/>
+  </symbol>
 </svg>