Update emojis to use harmony modules (import/export)

What does this MR do?

• Update native unicode emoji code to use harmony modules, import/export. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9570/diffs
  • Update main.js entry
• Got rid of side-effects
  • app/assets/javascripts/behaviors/gl_emoji.js
  • app/assets/javascripts/behaviors/gl_emoji/unicode_support_map.js

Are there points in the code the reviewer needs to double check?

• Should gl_emoji be a behavior still?
  • Should I move to app/assets/javascripts/gl_emoji or perhaps under lib?
• Should this go into 9.0? Probably not

---

✅ Currently running into some ESLint error. I created a separate issue for this https://gitlab.com/gitlab-org/gitlab-ce/issues/29160

Why was this MR needed?

Let's merge this 💪 This MR is big enough as it is, once we merge can you please use harmony syntax to import the needed modules please?

@filipa, https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9570#note_24881073

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1392

What are the relevant issue numbers?

n/a