Support emoji shortcodes in chat (#8455)

Completes: https://github.com/zed-industries/zed/issues/7299

Suggestions


https://github.com/zed-industries/zed/assets/53836821/2a81ba89-4634-4d94-8370-6f76ff3e9403

Automatically replacing shortcodes without using the completions (only
enabled when `message_editor` > `auto_replace_emoji_shortcode` is
enabled in the settings):


https://github.com/zed-industries/zed/assets/53836821/10ef2b4b-c67b-4202-b958-332a37dc088e






Release Notes:

- Added autocompletion for emojis in chat when typing emoji shortcodes
([#7299](https://github.com/zed-industries/zed/issues/7299)).
- Added support for automatically replacing emoji shortcodes in chat
(e.g. typing ":wave:" will be converted to "👋")

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Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>