[BUG] Render emojis in labels in issue info popup

- Currently emojis that are part of the label's name aren't rendered
when shown in the popup that you get when you hover over issue
references.
- This patch fixes that by rendering the emoji.
- Adds CSS to not make the emoji big in the label.
- Resolves #1531

web_src/js/vitest.setup.js

@@ -4,6 +4,7 @@ window.config = {
   csrfToken: 'test-csrf-token-123456',
   pageData: {},
   i18n: {},
+  customEmojis: {},
   appSubUrl: '',
   mentionValues: [
     {key: 'user1 User 1', value: 'user1', name: 'user1', fullname: 'User 1', avatar: 'https://avatar1.com'},