Add emoji autosuggest (#5053)

* Add emoji autosuggest

Some credit goes to glitch-soc/mastodon#149

* Remove server-side shortcode->unicode conversion

* Insert shortcode when suggestion is custom emoji

* Remove remnant of server-side emojis

* Update style of autosuggestions

* Fix wrong emoji filenames generated in autosuggest item

* Do not lazy load emoji picker, as that no longer works

* Fix custom emoji autosuggest

* Fix multiple "Custom" categories getting added to emoji index, only add once

spec/lib/emoji_spec.rb

@@ -1,15 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe Emoji do
-  describe '#unicode' do
-    it 'returns a unicode for a shortcode' do
-      expect(Emoji.instance.unicode(':joy:')).to eq '😂'
-    end
-  end
-
-  describe '#names' do
-    it 'returns an array' do
-      expect(Emoji.instance.names).to be_an Array
-    end
-  end
-end