Unicode rendering in user mentions '@' can sometimes cause usernames to not reflect what was selected

Issue Summary

Unicode is being resolved in the user mention, for example if you name was ὠilliam you'd be able to type your mention like @"\u1f60illiam" which is same as typing @ὠilliam.

However in case where there are two usernames \u1f60 and ὠ:

while typing \u in @ user mention the drop down selection shows the user \u1f60 (pre-render)

However once the comment is saved after user selection, it performs a post-rendering of the unicode characters giving a totally different result. It can either select a totally different user or render into a different unicode character failing the user mention.

This can cause user selecting one user but the unicode render converting it to a different user.

This is reproducible on Data Center: yes

Steps to Reproduce

• Have two users with usernames \u1f60 and ὠ respectively.
• Try to mention the user \u1f60 in any pull request.

Expected Results

• The dropdown selection will list the user \u1f60.

Actual Results

• Even though the user \u1f60 will be listed in the drop down, once selected and saved it will be rendered to the user ὠ.

Workaround

To disable unicode rendering need to escape using double backslash in the user mention.