Improve the @Mentions to work with the first letter of the name

It'd be good to improve the @Mentions functionality to work with the first letter of the first name or family name. In Japan, there are many users with just one letter as First Name and Last Name. Unfortunately, user with one letter as First Name and Last Name is not listed on suggestions of the @Mentions.

Steps to Reproduce

1. Create a user with one letter as First Name and Last Name.

2. In the editor, type '@' then "a" as the user's First Name or type '@' then "a b".

Actual Result

The user's name does not appear on the list of suggestions.
So a user with one letter as First Name and Last Name cannot be chosen from the suggestions list.

Workaround

It's possible to find the user with the username rather than the name.

Example:
Type '@' then "ab".