Major Description
When mentionning a user with `@` in CKEditor, there is a dropdown that displays to select a user, filtered on the start of the name already inputed.
This dropdown is not accessible.
1. There's no way to access it through keyboard navigation
2. The position in the HTML does not correspond to the position on the presentation.
3. Aria attributes are not set properly
Might need to check how it's done on other platforms such as Github.
