[lib/web/native] Show viewer in @-mentioning tooltip

Summary:
This enables users to see themselves in the @-mention tooltip so they can mention themselves. We won't have to make any changes to the user-profile on web/native since we already only just show the 'Message' button if otherUserInfo is undefined.

This does not need to be landed if we decide we don't want to enable this feature

This is part of ENG-6297

Test Plan:
Please see the videos below

Reviewers: atul, ginsu, inka, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10494