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

app/javascript/mastodon/features/ui/util/async-components.js

@@ -1,7 +1,3 @@
-export function EmojiPicker () {
-  return import(/* webpackChunkName: "emoji_picker" */'emoji-mart');
-}
-
 export function Compose () {
   return import(/* webpackChunkName: "features/compose" */'../../compose');
 }