Create an emoji plugin

[pomek]

📝 Provide a description of the new feature

This issue aims to provide a new CKEditor 5 feature called Emoji. As its name suggests, it allows for inserting emojis into the content.

There will be two ways to achieve goals:

1. By using the mention feature. Start typing : to trigger a mention dropdown.
2. By clicking a UI icon. It opens a dropdown that renders an external component. We need to listen for its events to pass them to the editor.

There is an npm package emoji-picker-element (https://github.com/nolanlawson/emoji-picker-element) that matches our needs. Could we use it to implement the feature we need?